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HYBRID ELECTRIC VEHICLES
Hybrid electric vehicles (HEVs) are a first step towards electric
powertrains, and generally consist of a conventional internal
combustion engine (ICE) combined with an electric motor. Their
main advantage is improved overall energy efficiency for the
vehicle in urban driving conditions and therefore a decrease in
fuel consumption and emissions, whilst simultaneously
guaranteeing appropriate range and performance.
HYBRID ELECTRIC VEHICLE CONCEPTS
Generally HEVs can either be classified depending on the
arrangement of their components or on their degree of
electrification. According to the component arrangement, it is
possible to distinguish between four vehicle concepts.
> Integrated starter generator (ISG) concept, the ICE is directly
connected to a generator and the driveshafts,
> Parallel hybrid concept, an additional clutch separates the ICE
from the electric machine and the driveshafts,
> Series hybrid concept, the ICE powers a generator and the
driveshaft is electrically driven and
> Combined hybrid concept, the ICE can mechanically transfer
the power to the wheels as well as electrically through a
generator and the electric machine.
For examining the functions of HEVs, it is more reasonable to
classify HEVs according to their degree of electrification (figure
1) as it is done in the following description.
Mico HEV
start/stop function
no e-drive option
Mild HEV
start/stop function
regenarative breaking
boosting
no e-drive option
Figure 1: Electric-hybrid powertrain concepts based on their degree of electrification
Full HEV
e-drive option (few km)
start/stop function
regenarative breaking
14 Austrian Technological Expertise in Transport
Micro HEVs mark the first step towards electrification of the
transport sector, They are conventional vehicles integrating a
new technique, known as the start/stop system. This system
automatically shuts down the ICE when the vehicle stops and
restarts it when the accelerator is pressed. Micro HEVs offer no
option for an electric drive or electric acceleration (boosting).
Their main advantage is that they can be realised with only
slightly increased costs. On the other hand they contribute to a
limited extent in decreasing CO 2 emissions. Available Micro
HEVs are for example the BMW 1 or the Citroën C3 Stop &
Start. Since this „light“ hybrid concept can be adapted easily to
a conventional powertrain it is expected that many
manufacturers will introduce this system in the near future.
Mild HEVs integrate an electric motor for assistance during
acceleration (boosting), which allows a smaller and more
efficient ICE. Furthermore, the electric motor acts in reverse as
a generator when the car is braking, recovering the kinetic
energy (recuperation) and charging the battery. Since Mild HEVs
do not allow electric driving, this concept similarly achieves only
small improvements in fuel demand compared to conventional
powertrains. However, they allow downsizing of the ICE without
any reduction in performance or comfort, with acceptable extra
cost. A number of manufacturers, such as Honda, Citroen,
Peugeot and Mercedes-Benz, are looking specifically at the
development and market introduction of Mild HEVs. Honda, for
instance, has launched the Honda Civic IMA (Integrated Motor
Assist) and the Honda Insight IMA, and Peugeot has developed
the 307 HDi Hybrid.
Plug-in HEV
e-drive option with
higher range
external charging
EV
pure electric drive