A contribution to cleaner vehicle technologies

Student thesis: Doctoral Thesis


Air pollution is an important concern for modern society as it induces important negative effects on the
living environment as well as on human health. Road transportation is identified as an important
contributor of this air pollution and therefore significant efforts are required to lower harmfull
emissions and consequently the impacts of road vehicles. Different vehicle technologies are being used
in road vehicles and each represent different characteristics with regard to emissions to the air.
Different fuels are being used as the energy carrier for vehicular application. Alternative vehicle
technologies are being developed such as hybrid and electric propulsion systems for road vehicles.
Several environmental problems due to air pollution of road vehicles, such as global warming and air
quality depletion, have been identified. When evaluating the environmental effects of road vehicles and
when comparing different vehicle technologies a clear and sound methodology for environmental
assessment is required. However, often incomplete or partial comparisons are used to evaluate
environmental performance of road vehicles. In this work the different sources of emissions and the
main environmental damages related to the use of road vehicles are described. An overview of different
possible vehicle technologies and potential policy measures is provided. Further in this dissertation a
new methodology for the environmental assessment of road vehicles is described. This methodology is
mainly used for an environmental rating tool for road vehicles. The rating tool allows ranking different
road vehicles based on their impact on the environment. In order to be able to compare road vehicles
with different power system technologies or using different kinds of fuels, a well-to-wheel framework is
used. In this way both tailpipe emissions and the emissions related to the fuel production phase are
taken into account. Different aspects of the environmental impact of the vehicle such as the greenhouse
effect, air quality depletion and noise pollution are integrated in the methodology. For this purpose, the
methodology includes four different damage categories: global warming, human health impairing
effects, harmful effects on ecosystems and noise. Further, the different impact categories are
aggregated and used to calculate a single indicator, called Ecoscore. The Ecoscore is a number between
0 and 100: the higher the Ecoscore the lower the environmental impact of the vehicle.
The applicability of the Ecoscore methodology is demonstrated with real vehicle data. From the analysis
made with this methodology, a positive evolution of the environmental performance of vehicles through
time is observed. This is mainly due to the ever more stringent European emission regulations. A low
environmental impact (and therefore a high Ecoscore) is obtained for a battery electric vehicle charging
its battery from the electricity grid. Also hybrid petrol?electric vehicles and the CNG vehicles obtained a
high Ecoscore. The LPG vehicle shows the best environmental performance amongst all conventional
vehicles, whereas Euro 4 petrol and diesel vehicles have a similar Ecoscore. When considering the
complete range of road vehicles on the roads in Belgium, the emissions of CO2 from more recent
vehicles, which were directly related to the fuel consumption, were not always reduced. The positive
influence of an improved engine technology is sometimes annihilated by an increase of the vehicles
weight or an increased energy consumption caused by certain on-board options. In recent years the
newest generation of diesel vehicles has caught up its delay concerning their environmental
performances on the petrol vehicles. Furthermore, the difference between the environmental
performance of those vehicles and the environmental performance of the LPG vehicles has been
reduced. The environmental assessment methodology was found to be robust and the environmental
indicator Ecoscore is thus applicable as a policy instrument (taxation, incentives, consciousness raising
campaigns, etc.) to support the use of environmentally friendly vehicles. The ambition of the Ecoscore
environmental rating tool is to lead to a common system for policy measures in Belgium and possibly in
other European countries, to promote the introduction and use of cleaner vehicles. The Ecoscore
methodology can also be used for the ranking of heavy duty vehicles and of two?wheelers. A calculation tool is developed and can be used to calculate the Ecoscore for a small set of vehicles available in the
tool as an illustration. Own vehicle data can be introduced and the different parameters of the
methodology can be changed by the user to investigate the influence of these parameters on the end
As was mentioned earlier, new technologies can be a solution to lower the impact on the environment
of road vehicles and of transportation in general. The well?to?wheel energy use and the environmental
impact of electric vehicles were found to be clearly lower compared to that of conventional vehicles (e.g.
diesel or petrol cars). In this context, light electric vehicles are in this context a promesing new means of
transportation and more particularly an interesting alternative for goods delivery. Many European
postal operators show interest for using these light electric vehicles for postal distribution. In particular
electric bicycles are found attractive for lowering the physiological stress of postmen during the delivery
of mail items. The introduction of automatic sorting machines in the postal business leads to an
increased availability of postmen for delivery within unchanged working hours. For this reason, the
delivery rounds can become longer with more mail items to to be distributed. Light electric vehicles
have a role to play in softening this increased workload for the postmen. Moreover, electric bicycles
allow ageing postmen to continue their mail and parcels delivery duty, hence limiting the social impact
of early retirement. Postal operators are also seeking to lower the total cost of ownership (operational
costs) of their delivery fleet and light electric vehicles and electric bicycles in particular are a promising
option to substitute thermal mopeds for instance. But also the raising consciousness of climate and
pollution issues, stimulate postal operators to continuously look for new and cleaner vehicles. However,
at the beginning of this research, most electric bicycles available on the European market did not satisfy
the requirements of the postal operators. In this context, a European project called NEPH was created.
An extensive questionnaire was performed by the department of Electrical Engineering and Energy
Technology to collect information on the requirements and wishes of the postal operators. From the
analysis of the feedback of the postal operators a set of main postal mission parameters that influence a
mail delivery mode were determined: total trip distance, number of stops on the delivery round, the
payload, cumulative height difference, etc. A first important result of this research was the translation of
the postal requirements into specifications for the sizing of the electric power system starting from
typical and available postal mission parameters. For this purpose, a calculation tool that uses an
approximate calculation method to estimate the required electrical energy of the power system has
been developed. This method uses the postal mission parameters as input parameters for the
calculation tool. The tool is illustrated by using it to calculate the required energy capacity of an electric
bicycle for typical postal delivery use. From the analysis a clear gap between the required energy
capacity for such a mission and the energy capacity from available (normal consumer) electric bicycles
was demonstrated. The calculation tool allows determining the required energy capacity in case of each
individual postal delivery round. Another way of using the calculation tool is to match or to optimize the
distribution rounds to the energy capacity of the battery pack that is used. Test rides with several
prototypes of electric bicycles for postal delivery have demonstrated that in case of demanding use of
the bicycle, the heating of the wheel motor caused the motor temperature to reach the maximal
allowable motor temperature. For this purpose, a thermal management system for the electric
permanent magnet d.c. wheel motor is proposed. The thermal management modulates the maximum
allowable armature current to the measurement of the motors temperature. This principle allows using
the maximal capability of the motor without causing sudden motor shut-down. Indeed, the maximum
armature current is only lowered in case of excessive heating of the motor. Overheating is prevented as
the armature current is progressively reduced with increasing motor temperature. An optimization of
the energy consumption of a power-on-demand power system, used for the NEPH power system, is
discussed. Postmen indeed tend to minimize their own contribution to the total traction power in case
of the NEPH power system. The optimization principle links the maximal allowable armature current of
the d.c. motor to the armature voltage. This optimization principle was implemented on new NEPH
controllers and validated on the road. An important reduction of 29% and 38% was obtained. This
solution allows to encourage the cyclist to deliver more biomechanical power as the contribution of the
motor to the total traction power is reduced with increasing vehicle speed. However, at start the
maximal traction force of the motor is still available and thus still allows lowering the physical stress on the postmen.
Date of Award27 May 2010
Original languageEnglish
SupervisorPhilippe Lataire (Promotor), Joeri Van Mierlo (Promotor), Peter Van Den Bossche (Jury), Jacques Tiberghien (Jury), Rik Pintelon (Jury), Jan Melkebeek (Jury) & Braham Ferreira (Jury)


  • ecoscore
  • environment
  • mobility
  • clean vehicles
  • vehicle technology
  • electric bicycle
  • postal bicycle

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