intelligent chassis systems in commercial vehicles - BME

intelligent chassis systems in commercial vehicles - BME
L. Palkovics
Intelligent chassis systems in commercial vehicles
INTELLIGENT ELECTRONIC SYSTEMS IN COMMERCIAL
VEHICLES
László PALKOVICS
Knorr Bremse Systems for Commercial Vehicles
Robert-Bosch-Str. 5
71701 Schwieberdingen, Germany
[email protected]
Abstract
Looking at the future trends of the road traffic, one will recognize that the commercial vehicle
participation will not decrease, although it is required from the environmental and social
viewpoints. The reason is that the other means of freight transport (water, railway, air) do not
provide the same flexibility as the road transport, and direct business interest of those
companies, who are using this transport form is larger than the eventual loss caused by the
penalties to be paid (taxes, compensation of higher axle load). This conflict is hard to solve,
but the effect can be minimized. The commercial vehicle industry attempts to introduce
systems to the vehicles, which are targeting on reduction of the environmental impacts caused
by heavy vehicles. These systems, which are named generally as “intelligent chassis systems”,
electronically control the operation of the chassis subsystems (engine, transmission, brake,
suspension) and co-ordinate their operation on a higher level (vehicle controller, intelligent
control systems, such as adaptive cruise control, video camera based lane change recognition
system, etc.). This paper reviews the state-of-the-art of the commercial vehicle chassis
systems, and tries to project their future development.
Keywords
Traffic safety, electronically controlled chassis systems, active safety, ITS, commercial
vehicles
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Intelligent chassis systems in commercial vehicles
1. INTRODUCTION
The automotive industry is one of the leading industrial branches all around the world. The
main reason of this fact is that this is the primary field of „civil” application of the newest
scientific results reached in the space, aviation and military research, as well as a good trial
opportunity for the new innovations in other scientific areas. No doubt, the passenger car
development, application of new ideas and technology is leading comparing to the other (road)
vehicle systems. The explanation for it is obvious: the price of passenger cars, usually bought
for pleasure rather than making profit, can incorporate the extra costs of the advanced systems.
This is the ground for the wide application controlled vehicle systems in passenger cars: ABS,
TCS, electronic engine control, semi-active and/or adaptive suspension controls are all
standard (options) in even medium size passenger cars.
The application of advanced, electronically controlled systems in commercial vehicles
somehow has not been as fast as in the passenger cars in the past. The explanation of this
situation shows the constrains for the development and marketing of these systems:
1. The primary reason why the commercial vehicle is purchased is business like:
making profit, which means low price of the vehicle, and low maintenance cost,
reliability throughout the life cycle of the vehicle. This fact is contradictory to the
application of any advanced system, since normally they make the vehicle more
expenses, although their impact on the vehicle safety, on the costs of operation is
obvious.
2. The commercial vehicle market is more conservative, does not like to accept new
systems unless it is convinced about the definite advantages. Typical example is the
reluctance of the market concerning the electro-pneumatic brake systems for heavy
commercial vehicles, whereas the advantages are obvious, but people "would not see
the brake actuation (i.e. there are no pneumatic lines, tubes, valves to control the
wheel brake) since it is done electronically. This was the reason (besides the
legislation) that redundant pneumatic circuits had to be installed in parallel to the
otherwise very safe electronic brake system.
However, with growing number of the vehicles all around the world the demand of the society
on the traffic safety is also increasing. Since the transportation infrastructure cannot keep up
with the rising number of vehicles there is severe task for the transportation as well as control
and mechanical engineers to control the traffic flow in the way of enhancing traffic safety and,
at the same time, increasing the efficiency of the transportation, i.e. increasing the traffic
density. As seen, there is an obvious contradiction between the mentioned two facts, since
increasing the traffic density will result in growing probability of traffic accidents. This
contradiction cannot be relieved, but it can be optimized by a certain way, giving intelligence
both to the vehicle itself, and also to the infrastructure, making the information flow between
the road and the car possible. The traffic flow control, however, cannot be solved only by
giving directions to the vehicle operator (by traffic signals, signs, etc.), since he/she is a human
being with all deficiencies of his/her nature: mood/age/sex dependent reactions, incorrect,
slow and delayed actions. As it will be seen later in this paper, beside the electronic control of
vehicle subsystems, such as engine, brake, the overall control of a single, or eventually more
vehicles is also possible.
These and similar requirements explain the need of the society for safer, less polluting, less
dangerous heavy vehicles, which have no significantly different performance as the passenger
cars. These facts make the development of commercial vehicle advanced systems more
interesting and more challenging for developing engineers and scientist, since to fulfill all the
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Intelligent chassis systems in commercial vehicles
technical conditions, at (relatively) lower price, resulting in a less complex system is not an
easy task.
2. SPECIAL PROBLEMS OF COMMERCIAL VEHICLES
As it was already mentioned, the design of commercial vehicle systems requires special attention
because of the different customer and social requirements. In this chapter some of these
differences will be considered.
2.1
Different Design Criteria of Commercial Vehicle Chassis Systems
As it was already mentioned earlier, the commercial vehicle industry operates on a different
platform as the passenger car industry. The design requirements are different, as shown in Figure
1.
Environment
pollution
ENVIRONMENT
RELATED
SPECIFICATIONS
DIRECTLY RELATES TO
PROFITABILITY
Cargo and
vehicle
safety
Vehicle op.
discomfort
Low cost at
buying and
during operat.
Communic.
with infrastr.
Damage to
infrastruct.
Transporting
hazardous
goods
VEHICLE/TRAFFIC SAFETY RELATED REQUIREMENTS
Figure 1
Design criteria of chassis systems for commercial vehicles
As seen in Figure 1, the general requirements for commercial vehicle chassis systems can be
divided into three main groups, which from design viewpoint have different weights:
1. The first group directly relates to the profitability (for which purpose the vehicle has
been purchased), which means:
•
•
•
•
•
transporting the cargo safely, without damage to the desired location,
reducing the duration of the transport,
purchasing the given vehicle at low price,
the system should be highly reliable, resulting in high lifetime and low cycle
cost,
the system should be simple enough to make the necessary maintenance
anywhere.
This group is the most important incentive in the development process: the
competitiveness of the manufacturers requires the optimisation of the overall vehicle
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Intelligent chassis systems in commercial vehicles
costs, i.e. reduce the component and their installation costs, utilise the possible
synergy in case of actuators, sensors, available data, provide value-added features to
the end customer. This very high cost sensitivity might result in compromises in
some of the cases, but this pressure brings also very innovative solutions, which are
technically also very interesting (for example the recognition of the roll-over danger
of the semi-trailer in a combination vehicle, as will be mentioned later).
2. The second group, which covers the vehicle/traffic safety related criteria, in some
sense in contradiction with the first group (e.g. high speed = higher efficiency, and at
the same time, high speed = lower traffic safety). From point of view of chassis
systems, the design criteria relate to the primary and secondary brake systems, the
suspension and steering systems. There are again contradictory conditions in this
group: optimising the primary suspension for cargo “comfort” (reduced vibration),
the road holding, and thus the safety of the vehicle is reduced and vice versa. The
wear compensation in electronic braking system (EBS) in in conflict with the proper
brake distribution among the axles of the vehicle. However, there are some primary
demands which has to be fulfilled without any trade-off: the brake system has to be
able to decelerate the vehicle by a proper reduction of the kinetic energy, and the
suspension has to provide the necessary force transmission from the wheels to the
chassis, improving vehicle stability in different manners (roll stability, yaw stability,
etc.)
3. The third group of requirements is formulated by the demands of the environment,
including the society as well. Generally, the systems cannot load the environment by
any means more than necessary or technically possible. The reduction of the
pollution caused by for example the brake pad materials, or the energy transmitting
substance, or the reduced noise and vibration caused by the wheel brakes, reduced
damage to the road surface are all desired by the human society. The driver’s fatigue
has to be reduced as well, which is a real problem in case of commercial vehicles
(see in Amirouche (2)) the long termed prolonged vibration to which the driver's
spine is exposed is causing severe illness after being in service for decades. The
reason can be found in the above mentioned contradictions: making heavy vehicle
front suspension “softer” (i.e. reducing the body acceleration), results in reduced roll
stiffness, which means reduced roll stability. Very important issue is the transport of
dangerous goods. The accident of such vehicles might results in severe loss in human
life, and long term environmental damage.
There is one more aspect, which belongs here: the legislation. In contradiction with
the passenger car industry, the commercial vehicle market and thus the industry is
more conservative, which is mirrored in the legislation. As an example, the first
trucks with EBS have been in the market for sale in September, 1996, but the 9th
modification of the UN ECE 13 Regulations, dealing with brake systems have been
effective since the beginning of 1997 only.
This short description is intended to give a little insight into the complexity of the problem.
2.2
Stability Problems of Heavy Combination Vehicles
The stability problems, and the resulting accidents of commercial, more specified, combination
vehicles, although their proportion in traffic is rather small in comparison with passenger cars,
always attract high publicity because of their severity (similar to aircraft accidents). When a bus
carrying 40-50 persons is involved in an accident, or when a 40 tons vehicle rolls over, they can
be found in the highlight of the media. To understand the special problems here, this chapter is
assigned to commercial vehicle accidents and the role of the driver in accidents.
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2.2.1
Classification of commercial Vehicle Accidents
The most dangerous motions of tractor/semi-trailer vehicle combination can be classified after
Verma et al (100) into three groups. The first type is called jack-knifing, which is mainly caused
by the uncontrolled large relative angular motion of the tractor and the trailer, which results in
the lateral slip of the rear axles of the tractor. The jack-knifing phenomenon is one of the most
common causes of serious traffic accidents in which tractor/semi-trailers are involved. The main
problem with this type of stability loss is that if the articulation angle exceeds a certain critical
limit, the driver becomes unable to control the motion of the vehicle by steering the tractor. Even
before reaching this critical angle, the problem may become worse if the driver steers the tractor
in an inappropriate direction. The aim of a control design is to prevent this critical situation from
developing. By using a suitable control strategy, the probability of jack-knifing can be decreased
and the possibility of inappropriate driver reaction exacerbating the situation can be avoided.
The second typical class of dangerous motions of articulated vehicles is the lateral oscillation of
the trailer, which may be caused by some disturbances (e.g., side wind gust, abrupt steering
effort by the driver) acting on the vehicle. When the design and/or operating parameters of the
system are close to the critical values, the vehicle becomes self-excited. This means that after
some disturbance, the vehicle loses its stability and the system's trajectory will tend to some
other limit set. In studies conducted by Troger et al (94) and Kacani et al (36) the non-linear
stability problems of tractor/semi-trailer combinations are discussed in detail and the vehicle
systems were investigated for their loss of stability. El-Gindy (17) and Woodroffe (112) have
proposed a set of safety-related performance measures, which can be used for heavy vehicle
design and regulation purposes. These performance measures also can be used for selecting a
suitable control strategy for a heavy vehicle.
The last typical reason for heavy commercial vehicle accidents is the roll-over. An interesting
statistics was found by Sarks et al (86), which is visualised in Figure 2.
Accident distribution for tractor/semitrailer
Type of accident
Driver error
3
Hit animal
16
1
Equip.malf.
Third party
45
Jackknife
7
Roll-over
18
0
10
20
30
40
50
Distribution [%]
Figure 2
Tractor/semi-trailer accident distribution (Source: Sparks et al (86)).
Based on the mentioned investigation, the roll-over accidents were categorised as follows:
• preventable, which means that the driver would have been able to avoid the accident
if a warning device had been installed on the vehicle. Only 3.3% of a total accidents
were judged to be preventable;
• potentially preventable, which means rollover might have been prevented depending
on the skill of the driver and performance of the warning device (38.4%);
• non-preventable, into which class the 49.7% of the total accidents were categorised;
and
• preventable unknown , which involves only 8.6% of the total number of accidents.
These statistics prove two facts:
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Intelligent chassis systems in commercial vehicles
• some of the accidents might have been avoided if the vehicle had been installed with
a warning system that would signal the driver to correct the vehicle's motion in some
appropriate way before roll-over occurs; and
• the majority (almost 50%) of the roll-over accidents would not have been avoided
with just a warning system as even a skilled driver would not have been able to
control the vehicle motion behind a certain point.
2.2.2
Driver’s Role in Accidents
The behaviour of a commercial vehicle driver is different as of the passenger car. The
commercial vehicle driver’s are aware of the weight and performance of their vehicles and these
are important factors in their decisions. While a fairly inexperienced – at least in comparison
with a professional heavy truck driver – reacts to a traffic situation very spontaneous, a truck
driver would evaluate the consequences. As an example, in some critical situation a truck driver
would not apply full brake because of being afraid of jack-knifing and its consequences (totally
uncontrollable vehicle), but rather having a rear-end collision with the preceding vehicle. Their
decision is made on the vehicle outputs that can be sensed directly. The vehicle outputs can be
categorised as either those sensible directly by the driver or those not sensible by the driver. The
signals belonging to the first class are primarily lateral acceleration, acceleration/deceleration,
roll angle (all of the tractor). The following signals cannot be sensed by a driver: the articulation
rate, roll dynamics of the trailer (especially if it is a full trailer), tire forces and several others.
The goal of the controller application is to measure or estimate these signals and react according
to both sensible and non-sensible signals to improve the performance of the vehicle. As an
example, Figure 3 shows a situation, which would definitely result in a rollover of the vehicle,
but the driver has very little information at the stage shown in the picture.
Figure 3
Typical stage before roll-over of a tractor/semi-trailer vehicle
By analysing the behaviour of articulated vehicles, one can observe that the driver’s steering
input is governed mainly by his/her reaction to the behaviour of the lead vehicle unit (tractor or
truck). Therefore, the behaviour of the towed unit(s) (semi-trailer or full trailer) in a real closedloop driver-vehicle system is not controlled directly by the driver. The other problem is that the
vehicle driver has only a limited number of actuators (steering wheel, accelerator and brake
pedal), that are not enough in all situations.
The other problems are the deficiencies of the driver as human being: delayed reaction, wrong
decisions, or disability to control the vehicle behaviour on the stability limits. The aim of a
controller design is to influence the motion of the combination according to the estimated states
of the articulated vehicle units.
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2.2.3
Intelligent chassis systems in commercial vehicles
How These Problems Are Handled?
As can be seen from the above analysis, the driver’s natural deficiency is one of the primary
cause of the traffic accidents.
1011
Information rate
[bit/s]
106
16
HUMAN DRIVER
SENSES
VEHICLE
ACTUATOR
SENSORS
SubConsciousness
Consciousness
MUSCLES
CONTROLLER
On-vehicle
sensors
Weather
Road
Intelligent road-side
systems, transm.
Figure 4
Traffic
Proposal for overcoming the driver’s deficiencies
As depicted in Figure 4, the driver’s action mechanism is rather slow. Although the driver
receives the information on a rather high rate (see in Glasner (26)), the muscle reaction will
become rather slow. The basic idea of the electronically controlled systems is to shortcut the
driver, and based on the same (or most) information, which go to the driver, take some action.
The variety of these actions is very wide: it starts with a simple warning until the full
autonomous control of the vehicle. In the main part of the paper these systems are classified and
their actual status will be given.
3. CLASSIFICATION OF CHASSIS ELECTRONIC SYSTEMS
Intelligent systems enhancing the traffic safety can either be only on-vehicle systems or
systems installed both on the vehicle and the infrastructure communicating with each other.
The former group includes already applied systems, such as ABS, ASR, anti-jackknifing
systems, and a series of newly invented systems making some of the vehicle subsystems
autonomous, producing a stabilizing effect on the vehicle without any activity of the driver, or
giving an early warning to the driver. These kind of systems are the drive stability systems
producing coordinated brake force, roll-over detection and preventing systems, or active 4WS,
having no feedback from the environment, but only from the vehicle. The IHVS (Intelligent
Highway-Vehicle Systems) also cover those solutions when the vehicle's on-board computer
receives information about the environment, road conditions and geometry, or about the other
members of the traffic flow and the on-vehicle systems, after processing these information,
activates some of the vehicle system to react to the external information. There is a wide
variety of such systems under development: platooning of the vehicles on the highway, to
improve the traffic density, intelligent following distance systems, navigation systems
transferring information to the vehicle about the traffic conditions and road data, etc.
The classification of the systems is shown in Table 1 as described below:
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•
•
•
Intelligent chassis systems in commercial vehicles
The first set of the systems are installed on the vehicle, obtaining information only
from the vehicle installed sensors, measuring the vehicle absolute variables (such
as wheel speeds, yaw rate, acceleration, vibration, etc.), but no information on the
road or the traffic. These systems can either be a driver's assisting ones, acting
when the driver conducts a certain maneuver, but the driver remains fully in the
loop. The other set of such systems is operating autonomously, based on measured
data, but without the driver's intention, and he/she can even be overruled.
The second main group differs from the former one in only one respect: they utilize
signals from vehicle mounted sensors obtaining information on the environment,
i.e. road, traffic, weather conditions. These systems can also act autonomously or
giving only assistance to the driver.
The third set of the systems uses information transmitted by transducers installed at
roadside. In this case the receptors are mounted on the vehicle, the information is
processed in the vehicle's ECU. The other way communication is also possible, the
vehicle can also transmit information to the public domain.
As seen in the table, besides the above classification, a further division of the systems is possible.
From the system autonomy viewpoint, the systems can be categorised as follows:
•
•
•
•
8
Driver triggered: the system requires direct actuation from the driver, and when the
measured state variables (wheel speed/slip, yaw rate) approaches the critical range,
the system will interact and modify these variable in order to increase the vehicle
safety. Such system is typically the passive 4WS, or the ABS.
They send a warning to the driver that some of the system variables are changed, and
indicate what the driver should do. Such systems are for example the vehicle
surround observing systems, which indicate audibly or visually an obstacle in the
vicinity of the vehicle when manoeuvring. There are systems, which belong to this
group, but they produce a slight counter-effect on the pedal or steering wheel,
indicating the direction of the proposed action, which might be taken by the driver.
However, this action (steering wheel rotation, or gas pedal push-back) is very small
and the driver can overcome easily their effect and consequently remains fully in the
control loop.
Some systems react autonomously, when they detect that the vehicle behaviour is
significantly different than a reference model calculated behaviour, and try to help
the driver to improve the vehicle stability. Such system is the VDC (Vehicle
Dynamic Control), which helps to realize the driver’s demand. It is very important to
note here that these systems do not oppose the driver’s intention, if the required
steering input is to the right, the system helps to go in that direction. This means that
the driver remains in the control loop even if the system intervenes autonomously.
The last group of the systems is when the driver is fully or temporarily excluded from
the vehicle control loop, the intelligent system makes decision and takes action
instead of the driver. Such systems are the lane departure avoidance systems, which
will intervene based on video input, or the control system when the vehicles are
platooning.
L. Palkovics
Table 1
Intelligent chassis systems in commercial vehicles
Electronic commercial vehicle systems and their classification
SYSTEM DESCRIPTION
System's operation only
based on signals measured
on the vehicle, no measured
information on the
environment, no information
received outside of the
vehicle
Information about the
environment and traffic is
used, sensors are installed
on the vehicle, no information
from vehicle-extern sources
are received
Information received from
external sources, such as
road infrastructure based
sensors, satellite, etc.
DRIVER’S ROLE
Driver’s intention is necessary
to activate the system, the
driver is kept in the control
loop
SOME EXAMPLES
ABS/ASR
Passive or speed
dependent 4WS
4WD
Suspension control
Power-train
management
STATUS
Already available
Already available
Vehicle condition
recognition
Roll-over detection
system, warning to the
driver
Under investigation,
some types exist
Some types are
available
Driver's intention is not
necessary, system is
activated autonomously, but
the driver remains in the
control loop
Active braking for
stability enhancement
(DSC, ESP, FDR)
Already available for
commercial vehicles
The on-board system gives
assistance or warning to the
driver, who remains in the
control loop
Adaptive Cruise
Control
Heading Control
Road friction
estimation for system
adaptation
Based on sensor signals the
safety system is activated
autonomously, the driver will
be excluded from the control
loop temporarily
(Remark: these systems can
also be used as warning, than
belong to above)
Radar Braking System Being investigated
Intelligent Cruise
Being investigated
Control
Lane departure
Being investigated
avoidance system
using image
processing
Information, warning is given
to the driver
Car navigation system
Electronic cornering
speed control via GPS
Road side transmitters
with curvature,
elevation data
Magnetic markers
transmitting warning to
vehicle about danger
Commercial vehicle
traffic control system
using GPS/GSM
Already available
Being investigated
Lane departure
avoidance systems
using reflecting
markers
Fully automated
system with roadside
communication
(magnetic markers)
Being investigated
Safety system is activated
autonomously
Already available
Already available
Already available
Active 4WS, additional Investigated, some
steering
available
Roll-over protection
Commercially
available
Already available
Being investigated
Being investigated
Being investigate or
partially available
Already installed
Some variants
available
Being investigated
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4. SYSTEM OVERVIEW
In this paragraph the detailed review of the systems listed in Table 1 will be given. One more
dimension for the classification will be introduced: the forces and moments between the tire
and the road determine the vehicle behavior and thus the stability, so the systems are grouped
further according to the wheel force direction. Thus the systems influencing the mentioned
forces in longitudinal, lateral and vertical direction are further divided. Of course, there are
sub-systems in the vehicle, which can have influence on more directions (such as the brake
system), these are considered separately.
4.1
On-Vehicle Systems - No Information on the Environment
4.1.1
Longitudinal Motion Control Systems
The longitudinal vehicle motion control systems are targeting on the improvement of the
vehicle ability of braking and accelerating. The brake, the power-train (engine, transmission,
retarder, clutch, differential) and the suspension systems influence the vehicle longitudinal
dynamics. Considering the vehicle safety, the brake system is the key element, so the
achievements in this field are introduced here in more detail, while the necessary sub-systems
of the power-train will be also mentioned until the necessary details.
4.1.1.1
Brake System
The braking performance and the behaviour during braking of the passenger cars and heavy
commercial vehicles significantly differ from each other. This difference in many cases has been
the cause for severe accidents because of different reasons: the longer stopping distance, the
higher response time of air-braked vehicles, much larger kinetic energy, intention for jackknifing are all dangerous in a traffic situations when both passenger car and commercial vehicle
are involved.
The commercial vehicles of the past used the compressed air as energy source and control
substance as well. The vehicle driver expresses the brake demand by pushing the brake pedal,
and his/her demand is transmitted to the brake chambers via several modifying valve assemblies
to achieve the desired brake force on the axles. Due to this fact, the dynamics of the air flow is
being modified and the system has different time constants, and exposed to large time delays, the
optimal control of the traditional pneumatic brake system is difficult to achieve. In addition, the
system is rather complex, contains many elements, complicated lining. The realisation of the
load dependent brake force distribution in pneumatic systems is a difficult task to solve. The
traditional load sensing valves operate based on the static deflection of the rear suspension, but
they are not able to compensate for the dynamic load transfer between the front and rear axles,
which might result in locking wheels or early ABS intervention on the rear axle. A further
problem is the condition of the trailer’s brakes. With bad condition of the brake system on the
trailer the motor vehicle has to compensate for the trailer brake deficiency, resulting in higher
brake lining wear, and overheating of the tractor brake system. This is caused by the
incompatibility of the towing vehicle and trailer brake systems. Although the application of the
auxiliary (not wear) brake systems, such as drive-line retarder, engine brake (see in Pressel and
Reiner (76)) will reduce the probability of occurrence of brake fading, and results in less lining
wear, their optimal operation requires certain experience from the driver. Another problem with
the conventional brake system is that there is no opportunity for system diagnosis, besides the
ABS self-test and the driver visual checks.
4.1.1.1.1 ABS/TCS System in Commercial Vehicles
The introduction of the ABS system improved the situation, but the until the vehicle does not
reach the higher slip region where wheel lock might occur, the ABS has no influence on the
brake performance. The commercial vehicle ABS systems became state-of-the-art, and also
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Intelligent chassis systems in commercial vehicles
mandatory almost all over the world. After the first generation, mostly feed forward like control
algorithm, the new generation has more advanced mostly closed-loop control algorithms. Due to
the low cost of a state-of-the-art ABS system, it became a popular platform for new functions, so
the assumptions of Emig et al (19) are fulfilled. A good overview of the ABS system
development is given by Leonard and Buckman (48).
The electronic load sensing (ELS) is one of these functions. In Europe and Asia the brake force
distribution between the front and rear axle, and also on the trailer is maintained by a load
dependent proportioning valve. This valve is a complex, expensive and maintenance intensive
valve, and also the provided brake force proportioning is not optimal. The new technology made
possible to use the ABS pressure control modulators for limiting the brake pressure on the rear
axle of the vehicle, thus providing the optimal brake force distribution. The basic idea of the
system is the so-called slip control, which means that the brake force distribution is optimal, if
the slip difference between the front and rear axle is minimal, that is:
∆s = (v2 - v1) / vabsolute ~ (v2 - v1) / v1 = 0
(1)
where v2 is the rear wheel, v1 is the front wheel speed. The principal operation of the ELS is
shown in Figure 5. This function is already available in passenger cars, however its realization
in commercial vehicles is not straightforward, since the loading conditions of the commercial
vehicles can
Brake light switch
v
Target speed RA
Actual speed RA
Vehicle speed
ELS
ABS
Estimated pressure RA
pmax
Target Slip
Figure 5
Proposal for overcoming the driver’s deficiencies
A similar new function of the ABS is the optimal brake force distribution when braking in a
curve, or the so call Drag Torque Control, which prevents the high slips on the drive-axle when
the throttle reduced abruptly by increasing the engine torque in order to maintain a wheel-slip in
a stable region.
There are markets, where the ABS is, and in fact, will be the wheel-slip control system, the
propagation of the EBS system will take more time. On these markets the ABS ECU is used as a
platform for other functions, such as fleet management, diagnostics, and similar function.
4.1.1.1.2 Electronic Braking System
The electronic brake system (EBS) targets on the elimination of the problems of pneumatic
brake systems mentioned before. The basic targets are as follows:
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Intelligent chassis systems in commercial vehicles
• to keep the compressed air, as energy source, but for the brake control electronic
transmission is used, i.e. the driver’s electronically measured brake demand is
transmitted to the valve blocks, which connect the reservoirs with the brake
cylinders. The time delay and the response time of the system is significantly
reduced, thus the stopping distance is lower.
• A more compact system will be achieved, with less components, with higher level of
system integration, resulting in lower installation costs,
• the signals, necessary for the optimal control of the brake force distribution are
measured electronically (rear axle load, wheel speeds, lining wear, etc.), thus more
accurate axle or wheel pressure control can be achieved,
• the tractor/trailer compatibility problem is automatically handled, adapts the control
algorithm to the trailer, and controls the brake pressures accordingly,
• resulting from the above features, the EBS is a safer, better performing brake system
with reduced stopping distance and enhanced braking stability,
• to provide a platform for future systems, such as adaptive cruise control (ACC), radar
brake system, drive stability control system.
At the moment, there is no unique EBS philosophy (unlike for ABS), there is no industry
standard. The EBS systems were already in development from mid of the eighties as seen in the
literature, but introduced in bigger volumes only after 1996. The brake by wire concept has been
introduced in the paper from Wrede, Decker (114), Straub (90) deals with the legislation
concerning EBS, and truck manufacturers reports their status in Wiehen, Neuhaus (104, 105),
Incardona, Moore (32), Stephan et al. (89), Winterhagen (110), Bassi (3), Beyer et al. (4). The
special aspect, the compatibility between the trailer and truck is investigated in papers from
Glasner et al. (27), Lindemann (50).
The available systems are differ from each other in the component arrangement, but the system
layout, control philosophy, data transmission, back-up principles, functionality are quite similar.
Figure 6 shows the simplified layout of the Knorr Bremse EBS 2 generation system, which is a
so-called distributed architecture system, since besides the central ECU, the axle/wheel modules
have also a small electronics, which provides an enormous flexibility of the system.
Figure 6
Basic EBS function
The brake signal transmitter, or the foot brake module has the same function as the previously
used pedal valve, namely to transfer the brake demand of the driver to the wheel brakes. In
fact, due to the back-up principle, the current EBS systems contain the same two independent
pneumatic circuits, which are controlled by the pedal valve in case of electronic failure. The
12
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Intelligent chassis systems in commercial vehicles
brake signal transmitter is assembled with double potentiometers in order to measure the
driver’s demand.
The ECU converts the measured deceleration demand into pressure demands, which are
transmitted to the axle/wheel modulators via the brake CAN (Controller Area Network). This
module is an electro-pneumatic actuator, in which the requested pressure is generated and also
the slip value of the actual wheel is maintained. The wheel speed sensor signal and also the
wear sensor signal is fed into the module ECU.
The electronic braking system provides the platform for many new functions, which are shown
in Figure 7. The block diagram illustrates the principal operation of the system as well.
INTELLIGENT
SYSTEMS
ON-BOARD
SYSTEMS
DRIVER
DEMAND
DRIVER AND EXTERNAL
SYSTEM BRAKE DEMAND
GLOBAL BRAKE DEMAND DETERM.
BRAKE BLENDING
ENGINE
BRAKE
TRACTOR
SERVICE
BRAKE
RETARDER
COUPLING FORCE CONTROL
BRAKE FADING
TRAILER
LOAD SENSING, WEAR CONTROL
FRONT AXLE
PRIM. DEMAN.
REAR AXLE
PRIM. DEMAN.
FRONT AXLE
FINAL DEMAND
REAR AXLE
FINAL DEMAND
ABS, ASR
PRESSURE CONTROL
LOOPS - EBS HARDWARE
FRONT AXLE
ACT. PRESS.
Figure 7
REAR AXLE
ACT. PRESS.
TRAILER
ACT. PRESS.
Block diagram of the EBS pressure modification logic
The EBS system functions, among others, are the coupling force control, which provides the
compatibility between the towing vehicle and trailer, brake blending, which means the
integrated control of all brakes (besides the wear brake), such as the engine, exhaust brake and
the drive-line retarder, wear control, which means the balancing of the wears between the
front and rear axle brakes. As it will be seen later, the feature of the EBS, that it is able to
produce brake force without the driver’s intention, is utilized in VDC and other systems.
Although the today’s EBS system has double redundancy (in addition to the electronic control,
there is a double circuit pneumatic brake system, the so-called 1E+2P system), the target is to
eliminate this because of cost and complexity reasons. The first target is to realize a pure
brake-by-wire system for control, but still keeping the pneumatics for actuation of the wheel
brake and, in a later stage, an electro-mechanic system, which actuates the wheel brake by
using electro-motors. In both cases the 2E system (in this case the pneumatic back-up is totally
eliminated, the system has 2 separated electronic control circuit) requires multiple and totally
redundant energy supply for control, and in the latter case also for actuation purposes.
Although the future system layout will look differently, Figure 8 shows a fully redundant
brake system, where every component is doubled. Of course, in the commercial systems the
wheel/axle modulators will not be doubled, since the regulations do not require that, but if the
brake control will be realized purely electronically, the double electronic circuit has to be
realized. This means two batteries, which are galvanically separated, and also separated
electronic circuits. While for the actuation of the wheel brakes the compressed air will be used,
the today solution with two pneumatic reservoirs is suitable. When the brakes will be actuated
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Intelligent chassis systems in commercial vehicles
electronically, the same double-circuit electronic system will provide the energy, which fulfills
the regulation (in fact, this system layout does not differ from the pure 2P system, same
redundancy is provided but electronically).
The electromechanical brake system is in the center of the passenger car manufacturers, since
the hydraulics is difficult to handle. Looking at the development in the field of the steering
systems it is clear: the hydraulics will disappear from passenger cars, and it will bring
significant benefits for the vehicle manufacturers from design, complexity, functional and cost
viewpoints. However in commercial vehicles this trend is not so clear, since the compressed
air is more friendly to produce and handle (there are no environmental issues) and as long as
the suspension of commercial vehicles (both primary and secondary) requires this working
substance, it will be used. Of coarse there are developments in the commercial vehicle brake
industry as well, but the tendency is more to move the components from the frame to the
wheel-end (axle, brake caliper, etc.) because of installation simplicity. The question rather is
how to fulfill this requirement, definitely one of the solutions is the electro-mechanical brake.
Figure 8
Fully redundant electronic brake system – theoretical solution
An additional important aspect, which determines the line of the development, is the fact that
the cabin should not have any pneumatic connection, because it makes the installation more
difficult since pneumatic tubes have to be brought up. This results in the fact that the today
pneumatic systems, having the actuators in the cabin (such as the parking brake, the trailer
brake in some countries) will go down to the frame and only the electric switch/potentiometer
will be in the cabin. It means electronically actuated parking brake or trailer brake. However,
this system requires a more advanced safety system.
4.1.2
Lateral Motion Control Systems
4.1.2.1
Steering System
For influencing the vehicle lateral motion the obviously used system is the steering. The
development of the servo-steering systems in commercial vehicles did not differ from the
passenger cars systems significantly in the past, until the hydraulics have been used for
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Intelligent chassis systems in commercial vehicles
powering the system. However the latest developments in passenger cars have shown clearly
that the hydraulics (as it was mentioned earlier) will disappear, since these systems will be
powered electronically and the development goes in the direction of the steer-by-wire system.
This trend in commercial vehicles looks differently, since the electric motor provided torque
might not reach the power need of the commercial vehicle steering with significantly heavier
wheel load. That is why the direction of development is mostly the electro-hydraulic steering
support, which can be applied for both front and rear axle steering system, and provides the
opportunity for driver-independent steering action, first at least in some limited range, but later
for full autonomy (see in Hughes, Elser (31)).
Steering wheel input
Side-slip angle on
the front axle
Side-slip angle on
the front axle
Side-slip angle on
the rear axle
Lateral force on the
front axle
Lateral force on the
front axle
Lateral force on
the rear axle
Yaw rate
Side-slip angle on
the rear axle
Lateral force on
the rear axle
Figure 9
Steering wheel input
Yaw rate
Yaw rate control
b.
Flow chart of the (a) front-wheel-steering (b) four-wheel steering systems
Rear Axle Steering
The front wheel steering does not give the optimal control, because of the time delay between
the steering (the lateral force appears first on the front axle) and the generation of the control
force on the rear axle, as the flow chart shown in Figure 9/a. Especially in case of longer
vehicles and in combination vehicles this effect is significant.
The high yaw rate of the vehicle results in enhanced danger of total loss of stability (the
vehicle spins out) on slippery road or at too high speed. With four-wheel-steering the lateral
control force on the rear axle is generated at the same time (see Figure 9/b) as on the front
axle, thus the vehicle yaw rate and lateral acceleration can be kept at lower values. In the 4WS
systems existing in the passenger car market the rear axle steering angle depends mostly on the
speed: at low speed the rear wheels are steered opposite to the front ones, improving the low
speed maneuverability, while at high speed the rear wheels are steered in the same direction,
which decreases the vehicle yaw rate. The active 4WS systems are able to react autonomously
to external disturbances, such as side wind gust. This means, when the vehicle is subjected to a
sudden side wind disturbance, the ECU measures the driver's intention (by a steering wheel
sensor) and the actual yaw rate, which differs from the calculated one, and compensates for the
disturbance with small rear axle steering. In this case the driver's action is not really necessary,
the system is acting autonomously, eliminating the driver from the control loop. The four
wheel steering has been examined as one of the possible vehicle dynamic control system, since
manipulation of the wheel slips on the rear axle has great effect on behavior of the towed
vehicle (trailer, semitrailer), as seen in many publications: Suzuki et al. (92), Watanabe et al.
(102, 103), Vaugh and Miller (99), Momiyama, Morikawa (54), Keller, Kogel (38) and Pflug
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Intelligent chassis systems in commercial vehicles
et al. (74). Stability analysis for articulated vehicles has been carried out by Chikamori,
Kawasawa (11) and combined with differential braking by O’Brien, Piper (60).
The 4WS in commercial vehicles has also an opportunity as shown in some publications of
already realized system. The control strategy of this system does not differ significantly from
the passenger car systems and provides definite advantages in high speed stability and low
speed maneuverability.
However, the serial applicability of the rear axle steering in commercial vehicles is
problematic from cost and design problems. To realize the steering of the rear axle with the
necessary control is simply more than doubling the cost of the front wheel steering. From the
design viewpoint the steering of the double-tired wheels, with that heavy axle load on the
driven axle (in case of tractors, for example) is a very difficult task. With the application of
super-wide tires this complexity will be reduced, the others remain.
In case of combination vehicles the trailer's axle(s) can also be steered to minimize the turning
radius, decrease the tire wear and improve high-speed stability. The so-called forced steering
is already state-of-the-art in some type of trailers (especially the long ones). The active
steering of the trailer wheels is also an option (TWS) and can bring quite a good improvement
especially in trailer handling, however the energy supply problems on the trailer and also the
complexity does not justify for that.
Front axle steering
The front axle steering will be modified also in the future. The electronic control for some of
the steering aid functions is also available today (for example the speed dependent assist
torque as in passenger cars), but there is a need for a certain autonomy in the steering system
as well. On a long term, the full steer-by-wire is the target, since:
•
•
this is necessary for advanced vehicle control systems, such as autonomous
driving, or vehicle stability control,
from design viewpoint it provides an enormous freedom for the constructors
since the mechanical link between the steering gear, which is on the frame and
the drive’s cabin does not limit this.
However the full (without mechanical link) steer-by-wire system has a severe acceptance
problem today, smaller from the legislation, definitely bigger from the end user side. The
scenario is more and less the same, as in case of the brake system, a double redundant
electronic system should provide the safety. However, while the brake system has 2 physically
separated actuator circuits (front and rear axle circuit) the steering has only one actuator,
which is not redundant (only its control and energy supply, but physically the actuator not).
This acceptance problem will enforce some interim solutions, where the mechanical link is
kept, but a certain freedom of the steering is given to the system, for example for lane keeping.
An interesting direction is the integration of the brake and steering based VDC system, which
operates based on the existing sensor signals (see below) and uses the steering system in the
silent (tolerance) range of the brake based system and contributes to the reduction of the
driver’s efforts during µ-split braking by additional steering.
4.1.2.2
Braking System Based Drive Stability Control
It was mentioned above, that the addition of a new steering system to the rear axle is
expensive, the full steer-by-wire has acceptance problems. Besides these, however, there are
technical problems as well: alone by the steering the whole longitudinal and lateral slip range
cannot be influenced, because of the nature of the system. This observation resulted in the fact
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Intelligent chassis systems in commercial vehicles
that other systems were taken into account for the vehicle stabilization purposes, which
overcome the mentioned problems. The brake system is the only logical consequence, since:
•
•
it has the most powerful actuators in the chassis (for example, 4 disk brakes in
a heavy vehicle are able to dissipate over 10,000 HP power), not only for
decelerating the vehicle, but also for controlling its lateral movement by
individual braking of wheels,
it is able to control the whole wheel slip range, as seen in Figure 10. The brake
system modifies not only the longitudinal, but also the lateral tire
characteristics as well, and thus provides the opportunity for the wheel slip
manipulation in all directions,
This fact was recognized by many researchers, and quite a lot of early publications can be
found: from Kimbrough et al. (40, 41), Palkovics et al. (61-68), El-Gindy et al. (18).
µ0
µ
ABS, or ABS in
EBS
Load Sensing
in ABS, or
normal EBS
function
DSC
and
ROP
ASR
Figure 10
Slip control ranges of the brake system
•
it is already installed on the vehicle, there is no need for new actuators and
partially sensors, the wheel individual braking can be realized by the EBS,
only very few additional sensors (steering angle, yaw rate, and acceleration)
are necessary.
The control logic of the DSC system in commercial vehicles is very similar to those in passenger
cars as shown in Figure 11, the only principal difference is that the commercial vehicle VDC
system controls also the brakes of the trailer in case of jack-knife dangerous situations (Figure
13/a). The major difference to passenger cars is that in trucks there is no need for extra
instrumentation to generate the driver-less braking, since the EBS provides that.
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Intelligent chassis systems in commercial vehicles
EXTERNAL SYSTEM DEMAND
ABS control range
DRIVER’S DEMAND
SENSORS
DECELERATION
DIRECTION
SENSORS
Longitudinal wheel slip
DSC
EBS
BRAKE BLENDING
CFC
LOAD SENSING
WEAR COMPENS.
CALCULATION
OF
DESIRED
MOTION
DSC control range
DSC
Modification
Longitudinal wheel slip
ABS, ASR
EBS WHEEL BRAKE ACTUATORS
Figure 11
Integration of the DSC into the EBS system
Yaw torque
necessary to
bring the vehicle
into the turn
Yaw torque
necessary to
bring the vehicle
out of the turn
Brake force applied
by the controller to
produce the
calculated torque
a.
Figure 11
18
b.
DSC intervention when (a) going into (b) getting out of a turn (wheel lateral forces are only for
explaining the phenomena, not for exactly reflecting the reality)
L. Palkovics
Intelligent chassis systems in commercial vehicles
Reduction of the lateral
force component on the
front outer wheel (high
slip value)
Brake
application on
the outer rear
wheel, high slip)
Reduction of the lateral
force component on the
outer front wheel (let the
wheel roll with high slip)
Releasing the inner rear
wheel to reduce the
lateral force component
and gaining reference
speed
Increasing the slip
on the outer rear
wheel
Trailer brake application
reducing trailer push or
causing trailer pull
a.
Figure 12
Overbraking the trailer
if necessary or possible
b.
DSC intervention in jack-knifing situation (a) without (b) with driver brake application
Palkovics et al. (69, 70), Petersen, E., Neuhaus, D., Glabe, K. (73) reports more advanced status
of the DSC systems in commercial vehicles. The original DSC concept concentrates on the
towing vehicle only, however the EBS on trailer provides also a platform for vehicle dynamic
control. In case of full trailers the yaw control of the dolly can be realized, and for longer
combinations (A and B doubles) the trailer EBS based system offers an alternative solution as
shown Fancher et al. (21, 22), or Lugner et al. (51). Chen, Tomizuka (9), investigate a
coordinated steering and braking controller in their works.
4.1.2.3
Other Lateral Control Systems
Besides the braking and steering systems, other systems have been investigated for controlling
the vehicle lateral motions. These solutions are mostly concentrating on the interface between
the truck and trailer, they intend to control the connecting force and torque. The hitch torque
control system uses a semi-active controllable damper to reduce the oscillation of the trailer
and functions as an anti-jackknifing device. The controlled lateral movement of the hitch point
is also an alternative solution, and can influence the trailer behavior. However these systems
are complex to install (design problems) and also their cost has to be considered. No doubt,
they can be used in some special cases (for example the jack-knifing device in articulated
buses of pusher type), their wide spread use is not quite possible. Kageyama, Saito (37),
Palkovics, El-Gindy (69) propose such solutions.
4.1.3
Vertical- and Roll-Dynamics Control
Unlike in passenger cars (although some recent cases has modified this believe) the vertical
and roll behavior of commercial vehicles is a very important aspect. The center of gravity of
commercial vehicles varies over a wide range depending on the type of the vehicle and the
cargo. The rollover of commercial vehicles is one of the most severe accidents, as it was
introduced earlier in this paper. In addition to the safety criteria, two groups of requirements
have to be considered: the economy and the environmental issues. The driver’s comfort and
the cargo’s security requirements contradict the environmental and safety aspects, and their
fulfillment is not quite simple.
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Intelligent chassis systems in commercial vehicles
The evaluation of the systems used for influencing the vehicle roll and vertical dynamics is
given in Table 2.
4.1.3.1
Electronic Leveling Control (ELC) System
The ELC systems have been available for heavy commercial vehicles for a few years. The new
generation ELC system is targeting on providing the traditional leveling functions, such as:
1. leveling function when loading or unloading the vehicle, with storable ramp
data,
2. fixed vehicle body position during traveling, which is optimal from point of
view of stability, comfort, etc. and depends on vehicle parameters such as
loading, vehicle speed, etc.
3. a certain delay, which means that the system does not operate continuously,
only in discrete time intervals it checks the suspension travel sensor values, and
corrects it, thus reducing the air consumption,
4. kneeling or discharging function, which is important in buses and tankers,
where the vehicle body is set askew (lateral and longitudinal direction,
respectively),
5. automatic as well as manual lift axle control, which hinders the driven axle
from overloading above the limits prescribed in the legislation,
6. start support operated by the driver, which means that the lift axle load, or in
case of tractor/semi-trailer the some trailer axle load can be temporarily
reduced to enhance traction,
and new functions, can be realized on this platform:
7. automatic traction enhancing function, which means the automatic lift axle load
release while the TCS is active. The ELC ECU receives this information from
the EBS via CAN interface,
8. lateral stability support, which is intended to increase the roll-stiffness of the
suspension while cornering.
As seen from the above functions, the ELC system is mostly practical but does not provide to
much of extra safety features. The new functions 7 and 8 are targeting on stability increase, but
due to the nature of the pneumatic system (large air quantities, time lag, etc.) they are not
effective in severe situations. Function 8 is able to compensate the body roll angle in a large
radius turn, but during a much faster lane change maneuver remains ineffective. However, the
ELC system with its sensors and actuators provides the platform for other suspension systems.
There are several solutions on the market and in research as shown in Schonfeld et al. (83),
Vogel, Claar (101), Glasner et al. (25), Goehring et al. (28), Kutsche et al. (44), Muijderman et
al. (56), Holdmann, Holle (30), Stein (1998), Bode et al. (5).
4.1.3.2
Adaptive Damper Control
The adaptive damper control system is not other but a semi-active suspension control system
using continuously variable shock absorbers. The control strategy for a semi-active damper is
not discussed here, since it is a state-of-the-art and can be found in many references (see in
Cole et al. (12), Muijderman et al. (57), Bode et al. (6), Isobe et al. (33), Roh, Park (77),
Novak, Valasek (59), Kitching et al. (42).
The application of the classical control strategies is not quite appropriate in commercial
vehicles because of cost constraints. This means that instead of the traditionally used vertical
accelerations at the body and wheel ends the already available signals are used for input to the
system, as seen in Figure 13. The damper control strategy has three preference levels:
20
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Intelligent chassis systems in commercial vehicles
• the third level preference is the cargo/driver comfort, this is considered as a
„default” setup. In most of the time (more than 95%) this setup is valid, in this case
the ELC system works as described above, the semi-active shock absorbers are
controlled by using a sky-hook principle.
• the second preference is the so-called attitude control, which means the vehicle
body pitch and roll control during braking/accelerating and cornering. In this cases
the shock absorbers are controlled in order to reduce the dynamic body roll and
pitch angle,
• the first preference is the vehicle stability, which means the support of the brake
system based DSC functions. If, for example, the DSC operates the brake on a
given wheel, the shock absorber on that wheel is switched to the maximum position
to provide the highest available tire force by means of reducing the dynamic tire
load.
vehicle speed
steering angle
brake/accel. demand
accelerations
ABS/TCS activity flag
yaw rate
axle-body
displacement
pressure sensor(s)
driver’s demand
Control of the
damping
coefficient
Figure 13
ADC ECU
CAN MASSAGES
FROM DATA BUS
STABILITY ENHANCING
FUNCTIONS
(ROLL, LATERAL)
ATTITUDE CONTROL
FUNCTIONS
(PITCH, ROLL)
RIDE/CARGO
COMFORT
FUNCTIONS
O
U
T
P
U
T
Adaptive semi-active damper control
As seen from Figure 13, the ADC system receives all input information from the vehicle CAN
bus, and requires no additional sensor signals. The ECU controls only the damper solenoids,
and as such, functions as a standalone system.
The above system exist also in pneumatic version, in this case the control of the by-pass valve
in the shock absorber is based on a pneumatic pressure (this is also a proportional valve). This
system is a rather low-bandwidth solution, since the pneumatic pressure is normally equal to
the air cushion pressure, which does not vary very dynamically. Normally the PDC (pneumatic
damper control) can be used in cases where it is enough to modify the damping characteristic
according to the actual load, for example for tanker trailers. Special design aspect, the road
friendliness is considered in the works of Vaculin et al. (96), Valasek, Kortüm (97), Valasek et
al. (98).
4.1.3.3
Cabin/Seat Suspension System
Due to the design problems of the primary wheel suspension system in commercial vehicles (if
the wheel suspension is comfort optimized, there is a problem with the load and road holding),
the driver’s comfort can be realized by the optimization of the secondary suspension systems,
21
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Intelligent chassis systems in commercial vehicles
such as the cabin and the seat suspension control. The reduction of the driver’s fatigue in
commercial vehicles is a severe issue since:
•
•
•
•
•
Low-back pain is one of the most common disabling health problem for
commercial vehicle drivers,
Low-back pain is the leading cause of industrial disability payments and
second most common medical cause of work loss,
Epidemiological studies indicate significant association of the low-back pain
complaint with seated vibration exposure and vehicular vibration,
Long term exposure to vibration can cause spinal disorders, fatigue, disk
raptures, vibration syndrome
Drivers, who had surgical treatment may be even more susceptible to adverse
effects of vibration and shocks.
These facts directed the interest of the truck manufacturers to the problem and started to put
more emphasize on the cabin and seat suspensions. The cabin suspension has a similar
structure as the primary wheel suspension (air-spring and shock absorber) and lately started to
use integrated solutions for leveling and also semi-active dampers. Further references to this
topic can be found in Savkoor, Mandez (81), Amirouche et al. (2), Wiesmeier, Uffelmann
(106), Lee et al. (47), Williams et al. (107).
However, there are some indicators, which show that the cabin leveling system will have no
long future. The opinion of some of the truck manufacturers is that the tilt cabin is not
necessary, since the vehicle driver or the road maintenance service is not in the position
anymore to make any kind of fixing along the road side because of the high complexity of the
vehicle electronic systems. Instead of repairing the vehicle along the road, they will be towed
to a certified workshop, where the cabin can be lifted off with the suitable equipment. This
means however, that for providing the proper working conditions to the driver, the seat
suspension has to be intensively developed.
The possible solutions for the seat suspension control are as follows:
•
•
•
•
•
Fully active suspension control – hydraulic cylinder or similar,
Control of the spring element – steel or air
Damper control – adaptive or controllable shock absorber
Continuously adjusted level – leveling control
“Intelligent” cushion – using special material in the cushion, which acts as
asymmetric damper, as produces variable resistance for the airflow through
the cushion material.
As an example the modification in the vertical acceleration transfer function is shown in
Figure 14, where pneumatic damper control is added to the actual seat suspension system with
leveling control.
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Intelligent chassis systems in commercial vehicles
2.5
Understructure/Floor
Seat/Floor
Understructure/Floor
Seat/Floor
2.0
Gain
1.5
PDC
1.0
0.5
0.0
0
1
2
3
4
5
6
7
8
Frequency [Hz]
Figure 14
Modification in the transfer function when PDC is used in a seat suspension
4.1.3.4
Brake System Based Rollover Protection/Warning System
As it was mentioned at the description of the ELC system, by means of compensating the level
variation in curve the danger of the rollover is not significantly minimized. The explanation to
that is given in Figure 15.
Without DSC
rolling over
Lateral inertial force
High C.G.
Longitudinal tire
force
Reduction in the tire lateral
force component
Lateral tire
force
With DSC a slight
lateral sliding
Longitudinal slip
Tends to zero by roll-over
Vertical tire load
Figure 15
Physics of the rollover and its recognition principle
The roll-over of a vehicle can start when the tire-road contact force on one of the curve-inner
side wheels becomes zero. This situation has to be detected or measured. However, a force
transducer for measuring the vertical wheel load is available or not feasible (there exist tiretread built sensors for measuring the tension in the tire tread for slip calculation, but they are
expensive and not really applicable). The roll-over responsible pair-of-force is arising from the
high lateral inertial force and its counterpart on the road, which is generated by the tire, the
23
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Intelligent chassis systems in commercial vehicles
lateral force component. If the CG point position is high, the resulted moment is also large and
can result in roll-over. From this it can be seen that only by means of the controlled suspension
the prevention of roll-over is not possible, since it cannot reduce the lateral tire force
component, the only (mostly theoretical, since it cannot be achieved by air suspension) effect
is to keep the vehicle body perpendicular to the road, thus eliminating at least the rolling
torque of the gravitational force.
Many different approaches can be found how to handle this problem, as seen in Cole (13),
Eisele and Peng (16), Dunwoody and Froese (15), Sampson and Cebon (80), Lin, Cebon (49)
and Winkler, Fancher, Ervin (108). A complete review of the available systems is given by
Winkler et al (109).
The basic idea of the roll-over protection and warning systems is if one cannot sense the
vertical wheel load directly, one has to find another quantity, which is in strong relationship
with the previous one and they vary together. This finding resulted in a system (see in
Palkovics et al. (72)) which stimulates the wheels via the brake or throttle system by applying
a test pulse in the brake systems or slightly reducing the throttle if the calculated lateral
acceleration exceeds a certain limit value (e.g. 0.4g). If this small effect produces high slip
difference between the left and right wheels, that means that one wheel is about to loose the
contact with the road. The described procedure gives the only direct indication of the wheel
lift-off. This information can be used either for warning the driver, or for intervention.
For the prevention also the brake system is used. As seen in Figure 15, the roll-over
responsible pair of force has to be reduced, which means the reduction of the lateral inertial
force by means of speed reduction with the combined reduction of the lateral force component
by means of manipulating the tire slip according to the figure. These two effects together are
enough to prevent rollover on both a combination and also on a solo vehicle.
The major advantage of this system is that it does not require any additional sensors to the
EBS, since it uses for detection only the existing wheel speed sensors and for actuation the
wheel brakes. The product itself is “nothing more” than software, however, the safety aspects
of the system are very complex, the original EBS safety management has to be modified
significantly. Of coarse, this system cannot provide 100% safety, but reduces the probability
of the occurrence of the rollover.
If the vehicle is equipped with DSC system, that system can also provide a rollover protection
function. The DSC estimates the loading situation of the trailer and makes an estimation of the
maximum permissible lateral acceleration. If the actual one exceeds this level, the system will
reduce the vehicle speed by limiting the throttle or also by braking. The integration of the ROP
into the DSC will result in a smoother function, but of coarse at the cost of all the sensors,
which are necessary for the DSC.
4.1.3.5
Tire Pressure-Monitoring Systems
As part of the suspension, the tire is also considered as one of the chief components of the
commercial vehicle safety. The appropriate tire pressure is a key of the vehicle stability and
thus the safety. In addition to the safety related aspects, the economical aspects are also
important: running with not a properly inflated tire the fuel consumption is also increased.
This topic has gained high importance lately, and the tire pressure monitoring system will be
mandatory in the USA. Basically two different solutions exist: either based on directly
measured pressure information, or indirectly, from the wheel speeds they calculate the
modified wheel diameter. Both solutions can be found in the literature, see for more details in
Rohr, Mendez (78), Mortensen et al. (55), Iwazaki et al. (34), Sakiyama et al. (79), Freigang
(23).
24
L. Palkovics
Intelligent chassis systems in commercial vehicles
The direct measurement of the tire pressure gives more precise indication, but results in a more
complex system, since the data transfer from the rotating wheel to the ECU is problematic.
The other solution is more straightforward, since uses the already available wheel speed
sensors, and does not require any new component besides the software (which can be
implemented in the ABS or EBS ECU), but less accurate, especially in case of tires with larger
profile.
25
L. Palkovics
Table 2
Intelligent chassis systems in commercial vehicles
Possible primary and secondary suspension control strategies
Main Group
VERTICAL AND
ROLL CONTROL
SYSTEM
SENSORS
ACTUATORS
ENERGY
DEMAND
SOFTWARE
PRICE
EFFECT ON
RIDE & CARGO
COMFORT
EFFECT ON
VEHICLE
STABILITY/ROAD
FEASIBILITY
PRIMARY
(WHEEL)
SUSPENSION
CONTROL
Electronic leveling
control
Pressure
sensor, level
and angular
sens.
Valve block,
servo valve
Medium
Relative
simple,
communic.
with brake
management
Low
Steady state
effect, no reaction
to dynamical
disturbances
Limited, mostly
influences the
steady-state roll
motion
There is a need for it
on the market
Adaptive air-spring
control
As for leveling
control, some
more is
possible
As for leveling
control
High
Complex,
communic.
with brake
management
Low
Improves ride/
cargo comfort
Reduces dynamic
tire load, road
damage
Feasible, has to be
investigated
Active or semiactive air-spring
control
Accelerometer
on the axle
and body
Modified faster
valve designed
for higher
pressure
Very high
Complex
High
Improves
sufficiently
Could improve
sufficiently
Not feasible
Fast (semi-active)
damper control
(electronic)
As for the
adaptive air
spring control
Third party
electronically
controlled
damper
Low
Simple, electr.
control to be
solved, can be
integrated
Medium
Improves,
response to
dynamic effects
as well
Improves road
Feasible, cooperation
holding and dynamic with damper
roll stability
manufacturer is
necessary
Slow (adaptive or
As for semilimited bandwidth
active damper
semi-active) damper control
control (pneumatic)
Pneumatically
controlled
damper
Low
Simple
Lower than
electronic
control
Improves roll/pitch Improves roll
comfort, slow
stability
effect
Feasible, cooperation
with damper
manufacturer is
necessary
Pneumatically
operated anti-roll
control
As above
Pneumatic
cylinder and
servo valve
Complex
High
Improves roll and
pitch comfort
Improves roll
stability and road
holding
OEM dependent,
feasible if low cost
Adaptive tire
pressure control
As above
Provided by a
supplier
Depending on
the actual
solution, low
or medium
Low
Integration is
simple
?
Improves ride
comfort in
average
Might improve road
holding (?)
Can be integrated into
ELC, cooperation is
necessary
Low
Complex,
Medium
information
from brake
management
should be used
Improves driver
comfort only
Influences traffic
safety via reducing
the driver’s fatigue
Feasible, question how
much the vehicle buyer
is interested in the
comfort of the driver
SECONDARY
SUSPENSION
CONTROL
26
Cabin suspension
Acceleration
control (semi-active) sensor and
or driver seat control angular sensor
on the cabin
Variable
damper, valve
block and
servo valve
L. Palkovics
Intelligent chassis systems in commercial vehicles
Integrated Chassis Management System
4.1.4
In order to achieve the optimal performance and cost level, the chassis systems in commercial
vehicles should utilize the synergic effect, which can be found in the communication among
each other. This system called integrated chassis management, has the following
characteristics:
•
has optimized number of sensors and actuators, since the information
exchange via the vehicle data bus is possible, thus lower cost and complexity
of the overall system can be reached,
the optimal performance of the system is possible to achieve, since the
operation of different controlled systems can be synchronized,
flexible system, since the integration of new systems can be achieved easily.
•
•
Air bag pressures (or
central pressure)
Intelligent
S ys tem ,
Fleet
m anam .
S USP ENSIO N M ANA G EM E NT
D isplacem ents
P rim . susp.
EC U
R oad side
transducers
Video signal
E LC
valve block
ECU
C entral E BS
ECU
R adar dist.
Sensor
A daptive
air bag
control
Controllable
dam per
(PDC/EDC )
Brake dem ,
VE HICLE
(D A TA B US )
Tire
pressure
m on.
Trailer
m odule
W heel
m odule
BR AKE M A NAG E M EN T
CAN 6
CAN 9
CAN 8
CAN 7
EC U
ECU
E lectronic
control
P neum atic
control
ECU
D R IVER
IN FO R M .
S YSTEM
EN G IN E A N D
TR A N SM ITTIO N
C A N data transf.
S ensor input
Figure 16
ECU
ECU
P edal
m odule
C A N 10
C om p.
control
W ear
CAN 1
ECU
A irdryer
contr.
C AN 4
C A N 13
ECU
AIR SU PPLY
M A NA G EM EN T
Steering
angle
W heel speed
C A N 11
P D C or
E D C for
cabin
P rot.
V alve
control
EC U
Steer angle
ES P EC U
int. sensors
CAN 5
CAN 3
C A N 12
Sec.s.
ECU
A ccelerat.
CAN 2
G P S signal
G S M C om m .
A nti-roll bar
control
Trailer E B S
STEER IN G
SYSTE M
D R IVER
Structure diagram of the chassis management system
Figure 16 shows the structure diagram of the chassis management system for a typical heavy
vehicle: 3 main systems are operated by compressed air: the air-supply, suspension and brake
systems. The air-supply system in traditional vehicles is controlled by pneumatic valves,
which do not provide optimal performance, and cause unnecessary air and energy
consumption. In the new generation of air-supply systems the control functions (such as the 4circuit protection valve, compressor, and air dryer) are achieved electronically, and due to the
communication with the brake and suspension system, the supplied air correspond to the
actual consumption of the systems (as an example, when the ABS is active the system
consumes more air, than during normal braking, which information is available now), and also
the brake system diagnosis becomes possible.
27
L. Palkovics
Intelligent chassis systems in commercial vehicles
The suspension control in traditional systems means only leveling, achieved by applying
pneumatic leveling valves. However, the performance of these valves is not perfect, and
causes high air consumption, since its reaction to dynamic suspension deflection cannot be
eliminated. The electronic leveling control systems do not have this problem, but besides the
electronically controlled leveling functions other, mostly stability and control related functions
couldn’t be realized. The information exchange with brake system, engine management makes
possible to adjust the suspension parameters according to the vehicle behavior in advance,
providing faster and more accurate control (sending the brake and accelerator demand and
steering wheel angle signals to the suspension ECU, which can react). An example for the
sensor number optimization: the EBS uses the rear axle pressure sensors, which is also
necessary for ELC - there is no need for redundant sensors, the signal can be transmitted via a
digital data bus.
The information exchange between the EBS and the engine, transmission management is already
used, however, it is currently being standardized using CAN interface. The communication with
engine management is two directional: the engine data (rpm, torque) are sent to EBS, while EBS
sends the desired torque value to the engine. Similar data exchange is conducted between the
EBS and retarder via CAN: the retarder control signal is transmitted from EBS, while the brake
torque and retarder temperature data arrive.
4.2
Intelligent Powertrain Concept
Although this paragraph disturbs the previously introduced structure of this paper, it is
important to mention this topic here, between the chassis and the systems, using information
from the vehicle environment. References to the intelligent powertrain topic are as follows:
Glasner (26), Powel (75), Winterhagen (111) or Borodani, P. (7).
The so called intelligent powertrain concept described by Spiegelberg (87) is based on the
separation of the decision making and actuation levels in commercial vehicles. This separation
is valid both for the hardware and also for the control hierarchy as well. The explanation of
this separation is given in Figure 17.
Control Level
New operating philosophy:
sidestick, ...
ACC, lane follower,
autonomous driving
Automation
of inputs
Collision avoidance
Predictive
input correction
speed vector
Execution Level
Translation to powertrain component inputs
Powertrain
co-ordination
ESP, ESP with steering
Reactive input
correction
Mechatronic subsystems:
steering, engine, transmission...
Figure 17
MMI
(Man-Machine
Interface)
Intelligent Powertrain Concept (Spiegelberg (87))
28
Execution
L. Palkovics
Intelligent chassis systems in commercial vehicles
The physical separation means the chassis of the vehicle contains all systems, which are
necessary to “move” the vehicle, that is to execute the commands from the control level,
which is physically the vehicle cabin with all the systems, which are necessary to determine
the demand for the “movement”.
The levels of the control architecture are assigned to this separation as well. On the control
level the inputs are collected and evaluated, if necessary corrected based on some future
information (predictive input correction), and a general speed vector is formulated, which
determines the necessary motion direction and magnitude for the vehicle. This speed vector is
transferred to the execution level, to the intelligent power train, which will realize this
requirement, and if necessary, corrects this based on past information (this is the so-called
reactive input correction). This speed vector is the connection between the paragraph 4.1 and
the next 4.3 and 4.4 parts of this paper.
4.3
On-vehicle Systems - Environment Information in the Control Loop
In a normal case the systems described in part 4.1 are actuated based on a rather simple speed
vector, the driver wants to follow the road and determines the direction (by steering) and
vehicle speed (acceleration or braking). The problem starts when the driver is not in the
position to determine the correct input, because his/her abilities are not enough for doing that.
In this case, if there are no additional information for modifying the driver wished speed
vector, the situation might result in a traffic accident.
If the driver does not pay enough attention, for example, to the vehicle or obstacle in front of
him the systems in the intelligent powertrain are not able to react or warn the driver. As an
example, the accident distribution related to the driver's falling asleep in different ranges of a
day is depicted in Figure 18. Due to the special working regime of commercial vehicles, this
type of accident is rather typical, and has been in the center of investigations for years.
FALL ASLEEP ACCIDENTS DURING A DAY
Distribution [%]
12
10
8
6
4
2
0
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
1
2
3
4
Period of the day [hour]
Figure 18
Distribution of the fall-asleep accidents during the day
As a result of falling asleep, the vehicle might collide with the moving or standing object in
from of it, or it can leave the lane, and might go to the opposite traffic lane or to the ditch. To
avoid such accidents, the modification of the speed vector is necessary based on additional
information. These systems will be introduced in this chapter. One has to note that the truck
and passenger car systems do not differ from each other very much from functional viewpoint.
However, there are some typical situations where commercial vehicle drivers are more
frequently involved than passenger car drivers (night driving, platooning for longer time, etc.)
so it is worth to point out the importance of these systems in case of commercial vehicles.
4.3.1
Longitudinal Motion Control
29
L. Palkovics
Intelligent chassis systems in commercial vehicles
The longitudinal motion control systems aim either on the collision avoidance of the standing
or moving objects in front of the vehicle or on the optimization of the traffic flow. The former
group includes the automatic brake systems, which scan the area in front of the vehicle and
calculates the vehicle's future motion, and either warns the driver or automatically actuates the
brakes, when it is judged to be too late for driver's action. The control logic of the radar brake
system is shown in Figure 19 adapted from Fujita et al. (24).
Radar
Sensor
Yaw rate
sensor
Longitudinal
acceler. sensor
Obstacle location calculation
Wheel speed
sensors
Vehicle future path prediction
Prediction of collision timing
Judgement of danger
Figure 19
Collision is judged to
be unavoidable
Collision is judged to
avoidable by the driver
ACTIVE BRAKING
WARNING
Schematic block-diagram of the radar brake system
The on-board system processes the radar information (relative distance and relative velocity to
the object), and from the yaw rate, wheel speed and the acceleration sensor calculates the
vehicle future motion. If the algorithm forecasts that the obstacle and the vehicle's path will
intersect each other it calculates the time until the collision. If the calculated time is in between
1.6-2.2 seconds, the algorithm will send a warning to the driver, because in this case the time
is enough for the driver to react. When the calculated time until the impact is less than 1.5
seconds, the algorithm will apply full brake pressure.
Although the idea is clear, the automatic (driver independent) application of brake system is
always a critical issue, since in this case the driver is eliminated from the control loop, since
he/she cannot reduce the braking effort. If in this case another type of accident happens, the
question will be asked: who is responsible. This is the reason that the manufacturers and also
the legislation are somewhat hesitating concerning this topic, although the technical
opportunity as we saw in the brake system paragraph is available.
To overcome this problem, for passenger car application a system is proposed by Naab,
Reichart (58)). In this case the control system gives only assistance to the driver, how to react,
but it does not act autonomously, which means the driver remains fully in the control loop and
responsible for the vehicle motion. In this case the vehicle is assembled with active accelerator
pedal, which is forcing the driver's foot into the correct direction, but the driver can easily
overrule the pedal. Further opportunity is the dynamic variation of the gas pedal
characteristics, which means that in speed critical situations detected by the controller the
pedal characteristic is shifted so that the driver has to apply it more to reach the same throttle.
The radar braking system is the basis for the intelligent or adaptive cruise control (ICC or
ACC) system (see for example in Fancher, Berekeit (20)). The aim is the minimization of the
distance between the following and the preceding vehicle. The potential of such systems is the
increase of the highway's traffic capacity at no increased danger of accidents. It also has a
positive effect on the decreasing environment pollution because it eliminates the low speed
"stop and go" traveling. It also increases the driver's comfort, thus reduces his/her stress, and
thereby decreasing the probability of traffic accidents. Figure 20 visualizes the difference
30
L. Palkovics
Intelligent chassis systems in commercial vehicles
between the driver controlled and ICC controlled platoon. The ACC system has high potential
in commercial vehicles. The heavy-duty vehicles are not dynamic participants of the traffic
flow as the much smaller passenger cars, consequently making overtaking maneuvers is not
very frequent. This means, however, that they drive normally in a platoon, which is very
stressful for the driver, and a potential source of accident.
This is the reason that the intelligent or adaptive cruise controlled systems are more and less
state-of-the-art, all vehicle and system manufacturers have their own system, as seen in the
following references: Chakraborty et al (8), Grace and Benjamin (29), Woll (113), Schiehlen
et al (82), Yanakiev, Kanneakpoulos (115), Powel (75).
Unstable
V
set
Free-flow velocity
(velocity is independent
of range)
Stable
ICC
control
Driver control
characteristic
V*
Stop & Go driving
d*
L
Distance (d)
Range (R)
R
d
Figure 20
Comparison of ICC and driver control of the platoon (see in Fancher, Berekeit (20)).
4.3.2
Lateral Motion Control
As it was mentioned before, the VDC systems offer enhanced steerability and stability for the
vehicle, but are not able to handle a situation when the driver's intention to steer is missing (e.g.
the driver is sleeping or late with his intervention). In such situations the vehicle has to have
information if there is an objects on the road in front it, to calculate its own future motion.
There are many systems under investigation, developed for driver assistance heading control,
whose operation mostly is based on lane recognition using video image processing (see in
LeBlanc et al. (46), Naab, Reichart (58) and many others). In the following part, a system
developed by the research team TU Budapest, Institute of Automation and Computer Sciences of
the Hungarian Academy of Sciences, and Knorr Bremse is introduced in more detail (see further
references in Soumelidis et al. (91), Kovacs et al. (43), Palkovics et al. (71)).
In order to detect the lane-departure, it is necessary to produce a robust estimation of the road
geometry in front of the vehicle. Three parameters have to be determined: the road curvature,
the width of the lane, and the vehicle’s lateral offset from the lane centre. The detection
algorithm is based on the optimization of two functionals.
Step 1: Estimation of the road curvature. The radius of the road curvature is relatively large on
public roads and highways. Thus the road section in front of the vehicle can be approximated
with a straight line. The detection system determines the angle α∃ between this straight line
and the front face of the vehicle. The perspective view of the roadway can be transformed to a
top view picture with parallel lane boundaries using equations of the perspective
transformation. Then a 2 N + 1 -dimensional array of the examined discretised angle range is
31
L. Palkovics
Intelligent chassis systems in commercial vehicles
defined: [− α N ,Κ ,0,Κ ,α N ] . An intensity profile vector p(α k ) is assigned to each angle α k .
This vector contains the sums of the grey-scales intensities in direction under angle α k
starting from the pixels of the bottom line of the top view road image. Next the vector
corresponding to α∃ should be selected. An optimisation problem is formulated for this task.
Another set of vectors δp(α k ) containing absolute values of the differences between elements
of each intensity profile vector p(α k ) is formed.
Then the angle α̂ is estimated as:
α̂ est = arg max δp(α k ) 1
(2)
αk
This method for estimation of the road curvature is independent of the type of lane boundaries.
They can be formed with solid or broken line lane marks, the lane boundary can be paved or it
can be a simple transition from asphalt to grass (or gravel). The curve on the left side in the
processed image of Figure 21 shows the estimated angle as a function of the time. The highest
bar in the lower of the two bar graphs above the trapezoid of the top view image shows the
estimated direction α̂ est , meanwhile the upper graph shows the corresponding difference
vector δp(α̂ est ) .
Figure 21
Input image and recognition of the lane geometry
Step 2: Estimation of the lane width and the vehicle’s lateral offset from the lane centre.
To solve these problems also an optimisation method is formulated which uses the result of the
Deriche’s edge detection operator applied to the input image. This powerful edge detection
operator was derived with the optimisation of three functionals characterising the noise
reduction, the localisation, and the uniqueness properties (4). The method for determining the
width of the lane and the vehicle’s relative offset from the lane centre is as follows. A pair of
parallel lines with angle determined in Step 1 are moved in the top view trapezoidal image (see
bottom chart on the Figure 21). The distance of the parallel lines is varying. The best fit to the
significant edges determines the needed parameters. This method can formalised as follows.
Let wˆ ∈ [wmin , wmax ] denote the width of the lane and oˆ ∈ [− wˆ 2 , wˆ 2] the vehicle’s
lateral offset from the centre of the lane. Let v(αˆ est , d , i ) be a vector of the length d under the
estimated angle α̂ est starting from a bottom line pixel of the top view image (formed from the
result of the Deriche’s edge detection operator applied to the original image) shifted from the
32
L. Palkovics
Intelligent chassis systems in commercial vehicles
centre pixel by i points to the right. v j (.) denotes its j th element. The parameters w∃ and o∃
can be estimated using the following formulae
oˆ est = iopt −
wˆ est
2
(3)
where
[wˆ
]
est , i opt = arg
d
max
∑ v (αˆ
w∈[wmin , wmax ]
j
est , d , i
− w)v j (αˆ est , d , i )
j =1
i∈[0 , w ]
All the estimated parameters have been filtered with a 2nd order Butterworth filter to achieve
better performance. The second and the third line from the left on the Figure 21 show the
vehicle’s lateral offset from the lane centre and the estimated lane width. The presented
optimisation procedure can be easily generalised to higher order curves approximating the lane
geometry in front of the vehicle.
The above described algorithm has been tested under several environmental conditions (wet
road, dirt on the surface, road signs, during night, partially covered by snow, etc.) and the
robustness of the system has been surprising. In this form the system is appropriate to detect
the road edges, but it is not suitable for identifying other objects on the road. The investigation
is expanded in the direction of the stereovision.
The video signal can also be used for other purposes: the so-called drowsy driver detection
system (see in Grace and Benjamin (29)) is installed in the vehicle and observes the driver’s
eye-lid motion. When the driver is close to sleep, the frequency of the eye-lid movement will
be reduced, and it can give indication to the controller to take some action. The question is
what that action can be. The opportunities are the same as above: either to warn the driver by
acoustic or video signals, or to provide an indication, what he/she has to do, or to intervene
into the vehicle control and take steering or braking action. The problem is the same or even
more severe, as in case of the cruise control systems: who has the responsibility. The
indication of the proposed direction by means of applying a slight steering torque on the
steering wheel is an opportunity, especially when the vehicle has a steer-by-wire system or
electric power assisted system. In this case the driver will recognize that there is a dangerous
situation and will intervene.
The other definitive opportunity is the autonomous control by means of steering, or also by
unilateral braking. A proposal for the VDC integrated system has been made by Palkovics et
al. (71). The control loop of the proposed intervention is shown in Figure 22.
33
(4)
L. Palkovics
Intelligent chassis systems in commercial vehicles
steering, brake, throttle
road scene
DRIVER
warning
lanerecognition
comparison
DECISION
DSC
system
VEHICLE
states of motion
trajectory
prediction
view of the road from the vehicle
Figure 22
VDC integrated lane departure avoidance system
The brake system has enough power to control the vehicle’s lateral motion and, at the same
time to reduce the vehicle speed. Since the situation in this case is considered as understeering,
the controller will apply the rear wheel brake, which means that the driver will not be
disturbed. Video images of a typical situation can be seen in Figure 23/a, while Figure 23/b
shows the related state variables of the vehicle and the controller.
Figure 23/a Vehicle behaviour during intervention and the resulted behaviour
34
L. Palkovics
Intelligent chassis systems in commercial vehicles
12
front left wheel speed [m/s]
10
front right wheel speed
8
6
pressure of the right rear brake chamber [bar]
4
2
trigger from the vision system
0
yaw rate of the vehicle [0.1/s]
-2
60
60.5
61
61.5
62
62.5
63
63.5
Figure 23/b Vehicle’s and the controller’s state variables during the manoeuvre
4.4
Systems Using Off-Vehicle Information
The systems have been described in the previous parts of this paper had all the installation on
the vehicle, they were not receiving any external information. In some of the cases, however,
those information are still not able to guarantee the safety of the traffic flow and the individual
vehicle. There are certain attempts around the world to increase the number of available
information about the road segments, weather, etc. There are many projects, which deal with
the research of intelligent highway vehicle systems. Such a project was the European
PROMETHEUS, or the North-American PATH. As outputs of these projects, several systems
were proposed or partly realized; these are not discussed here.
Just a typical example, the majority of roll-over and spinning out accidents happens during a
turning maneuver, when the speed of the vehicle is not correctly determined. The ramp leaving
the highway usually has a decreasing turning radius, so when it is negotiated with constant
speed a sliding out or roll-over can occur. There are several proposals that the vehicle driver or
the on-board computer should be aware of the radius of the turn. If this information would be
available, the VDC unit is able to calculate the maximum speed, with which the turn can be
taken without any kind of stability loss.
The major question here is how to transmit these kind of information to the vehicle, do we
really need to modify the road infrastructure, or is there another solution. The road and related
infrastructure are normally built for longer time intervals (decades) without having any major
restructuring during this period. This means a very rigid structure, since parallel, the
technology is developing with much higher speed. This conflicting fact causes that the early
attempts to make the road infrastructure intelligent are shifted now to the non-road related
systems. With the current level of telecommunication, telemetry offers an ultimate solution to
overcome this problem, and provide a much more flexible opportunity for the intelligent traffic
control systems.
4.4.1
Commercial Vehicle Fleet Management System
The fleet management system for a freight cargo company is not an option, but a must. To
provide the optimal utilization of resources, finding the optimal roots from point A to point B,
to provide the safety and security of the vehicle and the cargo these are all tasks for the fleet
management system. There are many systems and methods available already for solving both
the technical and also the logistical problems. Some of them are listed also in the references
under the title of fleet management: Taniguchi et al. (93), Mato (53), Jung and Haghani (35)
35
L. Palkovics
Intelligent chassis systems in commercial vehicles
offer solutions to the vehicle routing problem, Luettrignhaus (52) introduces a telematic
system for fleet operators, or An and Jung (1) proposes a radio communication based system
for providing the fleets with freight and traffic information. These are only few examples one
cannot really review all the publications published in this field because of the enormously high
quantity.
What is very important to recognize here is the following: the reserves of further optimizing
the costs of the freight transport, reducing the safety of the traffic, producing less load on the
environment based only on the vehicle development, are more and more declining. Both active
and passive safety of the vehicle are reaching their limits, the VDC systems, the electronic
braking, the vision system all provide the maximum available safety today. The road friendly
suspension, the super low emission engines are generating the least today possible load on the
environment. Of course, there is a lot to do, but a significant jump cannot be achieved only
from the vehicle side.
The potential of the qualitative change is in the communication, between the vehicles, with the
infrastructure, and also with the information system controlling the traffic flow. The principal
block diagram of the fleet management system is shown in Figure 24.
Off-board
On-board
COMMUNICATOR
MANAGEMENT CENTER
Different means of
communication: GSM,
Satellite, Radio
(Data collecting, storage,
statistical analysis, data
forwarding, etc.)
GATEWAY
Between the vehicle and
the communicator
External
World
Internet
WAP
GSM
GPS
RFID
ISDN
Links to:
• Own display
• Driver’s info display
• Off-line download of
registered data
EBS,EDC,Trailer EBS..
VEHICLE
With intelligent chassis
systems – access to data
available on veh. network
Figure 24
Structure of the fleet management system
As seen in Figure 24, the fleet management system has 3 major parts:
•
•
•
The on-board system, which is in the vehicle,
The off-boards system, which is the fleet management center,
The 3rd part is the information, which can be obtained from public domain or any
third party system.
In the next paragraphs some details of these systems will be given.
4.4.1.1
The On-Board System
The vehicle on-board system can be further divided:
•
The electronically controlled vehicle systems, which were analyzed in the
previous parts of this paper, such as chassis control system, intelligent systems,
etc.
36
L. Palkovics
•
•
Intelligent chassis systems in commercial vehicles
The so called communicator unit, which serves for the positioning and also for the
data transfer between the vehicle and the management center, or other 3rd party
systems (for example for the inter-vehicle communication),
And the gateway, which solves the data interchange between the vehicle and the
communicator.
The communicator includes both the vehicle positioning, as well as the data transfer form the
vehicle in motion. Analyzing the developments in this field, the potentials are tremendous.
For the positioning system the following alternatives exist:
•
•
•
•
GPS - satellite based position information, in standard form, which can be
transferred into any other format. Precision is in the 10 m range or below, since the
civil purpose satellite information are not disturbed anymore
DGSP - differential GPS, which improves the precision of the normal GPS
information by means of using a fixed-point information broadcasted by a radio
station. Very high precision can be obtained, if necessary for special applications
(for example guided bus system door positioning and the stopping stations, or
automatic backwarding system for multi-unit vehicles)
MPS (Mobile Positioning System) - a localization system using GSM network
developed by Ericsson. The precision of the location information is in the range of
100-130 m, which might be suitable for some applications,
Satellite photo can also be used for positioning, however for on-line applications the
feasibility is questionable,
For the communication system the today available solutions can be listed, but this field is
developing so rapidly, that this list might be modified until the appearance of this paper:
• Radio networks - in short ranges the radio network can be used for data transfer,
however, the effective range is small (40 km), data receiving frequency is high, but
no roaming is possible.
• Analogue radio phone (450 MHz) - data receiving frequency is smaller, locally
viable, no roaming is possible, but provides a cheap solution. For domestic or local
fleets (such as bus companies) offers a cost efficient and reliable solution.
• Generation 2 GSM - the today’s system - both direct data transfer, as well as SMS is
available, roaming is possible. The direct data transfer is expensive, the SMS is
cheaper and the system has relatively low bandwidth (15 kbit/sec), which does not
make some on-line control options possible.
• G2.5 GSM system, which is a intermediate solution, with some new functions,
which are interesting from the fleet management viewpoint:
• GPRS (General Packet Radio Service) based on packed information transfer the user pays after the transmitted information amount (not the time), high
bandwidth is available (up to 115 kbit/sec), TCP/IP communication (always in
connection), parallel voice call is possible, already available in 2000.
• EDGE (Enhanced Data rates for Global Evolution) - using the above network
infrastructure, the EDGE is a combination of a high speed modulation and
GPRS technology. Depending on the application, 384 kbit/sec bandwidth will
be available in 2001.
• G3 - 3rd generation GSM phone system with high bandwidth (2 Mbit/sec), and
voice, picture, data package parallel transfer will be available. Appropriate for online control. Start of the availability in test systems in 2001/2002.
37
L. Palkovics
Intelligent chassis systems in commercial vehicles
• Closed networks, today available only for closed applications (police, military, etc.);
civil application is under development. Such a system is the TETRA, which can
send SMS like messages without disturbing the normal voice communication.
• Data transfer via satellite - existing opportunity, data is being transferred from a
mobile unit via satellite to a ground unit, which uses normal ISDN to send the data
to the host computer. The Inmarsat D provides this service.
• Data download when vehicle is back to the home base, or reaches points with such
terminals: high bandwidth infra red data transmission (IRDA) and similar
As it can be seen, both for communication and positioning there is a wide variety of systems,
with different performances available. It is very difficult to see, what will bring the future. For
the today’s application for communication the GPS positioning + GSM SMS for data transfer
is used. The reason is the simplicity and the relatively low price.
Important part of the system is the gateway. Its importance is not in the technology, since it is
relatively simple. The problem is the accessibility to the vehicle data. Until the system has to
solve only the positioning and some general data transfer of the position and speed
information, the system does not require any communication with the vehicle. However, the
vehicle and cargo security, the traffic safety, the vehicle economy require very intensive
communication with the vehicle data bus, which is already problematic. These data on the
vehicle has a specific owner (vehicle or system manufacturer), who wants to utilize these in
order to “sell” them to the end user, who can optimize its transport process, consequently
make money with it. There are attempts to standardize the accessibility to these data, today
without success.
4.4.1.2
Off-Board System and Service
The advanced fleet management system should offer functions to the fleet owner, which has
certain $-value. That means that the fleet applies some of the function packages, that should
bring benefit to the owner. For that purpose, several function groups can be defined as seen in
Figure 25, like traffic management, safety, diagnostics or cargo security package. Of coarse,
the availability of the functions of these packages depends on the technical level of the system
(complexity). Just a few examples: route optimization is possible based on the actual
geographic information, however, if there is no actual traffic jam information, the previously
defined route might not be the best one, or if there is a warning of misuse of the vehicle to the
management center (continuos overspeeding, high lateral accelerations) the vehicle speed can
be remotely limited via the communication to the engine management.
38
L. Palkovics
Intelligent chassis systems in commercial vehicles
Functionality of the system
Traffic
manag.
pack.
Safety
package
Economy .
pack.
Diagnostics
pack.
Cargo
security
pack.
On-line actuation
some systems
Complexity of
Limits some
the system
functions (speed, gas)
Audio/visual info, not safety related
actuation
AVL + Communication with vehicle
system, vehicle data transfer.
Automatic Vehicle
Location (incl. communication)
Figure 25
Functionality of a fleet management system with different complexity levels
These are just a few examples what can be achieved with such systems, definitely it will
rapidly develop in the future. What is going to give a big push to this field is the fact that also
the vehicle manufacturers recognized the value of the information from their own systems, and
besides selling only the vehicle, they started to sell also service, one of them is the fleet
management, at different levels. With the development of the communication systems outlined
above, the commercial vehicle behavior will be monitored and exact on-line information will
be available for the owners (of the vehicle and of the cargo as well) about the actual status of
their property.
5. CONCLUDING REMARKS
The target of this paper was to summarize the actual status of the commercial vehicle chassis
electronic systems affecting the vehicle and traffic safety. The basic conflict, that on the one
hand the vehicle is produced for making return on the investment and thus has to fulfill very
severe economic requirements and on the other hand, because of the society/environmental
constrains, it has to fulfill high technical requirement, resulting in a very rapid development
during the last decade. While 15 years ago, the studies have shown that the basic design of an
average truck did not differ significantly from the design at the beginning of the Second World
War, a top class heavy vehicle of today is technically at least as advanced as the best passenger
car. In the fields of safety, stability, environmental compatibility and comfort the commercial
vehicles are competitive with passenger cars.
The intelligent systems outlined in this paper are mostly taken over from passenger cars and
adapted to the special truck environment, but there are also systems, where commercial
39
L. Palkovics
Intelligent chassis systems in commercial vehicles
vehicles were more advanced, for example the electro-pneumatic braking system is available
in trucks since 1994, and today all heavy vehicles are assembled with EBS. The electrohydraulic braking (analogue to EBS) is under development in passenger cars. Definitely, the
developments in technology, electronics, navigation and the related fields make this rapid
development possible, and it projects a very exciting future. It is possible to realize a fully
autonomous commercial vehicle even today, which has only electronically controlled systems,
starting with steering, braking, engine management, transmission. Those, who visited the 2000
IAA (commercial vehicle exhibition) in Frankfurt, Germany can remember the presentation of
the DaimlerChrysler PTU: the visitors could drive a truck in Hannover from a driver’s seat in
Frankfurt. That means the technology is already available, perhaps yet not as developed as it
would be required, but the tendency is clear: it develops towards to the fully electronically
controlled systems in commercial vehicles.
As a conclusion, the image of heavy vehicles as the “road-eater ugly monsters” is being
changed.
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