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planetary gear unit, BMW, Daimler and GM, on the other hand use
two planetary gear units, clutches and brakes. VW, Audi and Por-
sche position the electric motor between the clutch and a conven-
tional automatic transmission.
Depending on the electric motor concept, a manual transmission
is neither required for start up, nor for the maximum speed. Com-
pletely dispensing with a multistage transmission is only possible
for high-torque machines. A simply built and inexpensive step-up
gear unit suffices for these concepts. However some development
directions have high-speed motors that require a stepped trans-
mission. Multi-step transmissions are frequently designed simply
as two-step transmissions. In general, dispensing with the com-
plex transmission components contributes to reduced costs and
an increase in efficiency of the entire propulsion system. Hybrid
vehicles usually require a more complex and very sophisticated
and expensive transmission unit, while battery electric vehicles
usually have simple and thus inexpensive solutions.
In today’s combustion engines the auxiliary aggregates are almost
exclusively operated with a constant ratio of transmission to the
crankshaft. The supply of energy to these components must be
ensured and taken into account in any overall consideration. They
account for 20 to 25 percent of the mechanically executed work
and thus approximately 7 percent of the total energy of a vehicle
[see. A. Friedrich (2007) for example].
Currently a number of auxiliary aggregates are necessary to assu-
re the functional capacity of a combustion engine (lubricating oil
pump, coolant pump, fuel delivery system, radiator fan, mechani-
cal charger) or implementation of exhaust cleaning (secondary air
pump, catalytic converter preheater). These are not required for
battery electric vehicles. However other aggregates that are pow-
ered by the combustion engine cannot or should not be dispensed
with in battery electric vehicles such as the power steering pump,
the vacuum pump for boosting the brake force, the ABS, the ASR,
and the automatic leveling system. If the combustion engine is
removed, these components must either be electrified or electric
auxiliary motors must be installed, which can be used in a manner
that fulfills the requirements and that can be operated in a manner
that is optimized for consumption. For example, innovations are
needed for steering systems (electro-mechanical solutions, „steer-
by-wire“ concepts) for combination recuperation via the generator
and for friction brake systems or electromechanical brakes).
It must also be remembered that the entire energy required for the
auxiliary aggregates needs to be provided by the main battery of
the vehicle. This reduces the energy available for pure driving, and
thus it reduces the range to a considerable extent. It must also be
remembered that a new acoustic design will be required for the
electric auxiliary aggregates. Previously this could be omitted be-
cause the combustion engine provided a permanent background
noise, even in idle, and for the user it drowned out possibly unple-
asant noises generated by the electric auxiliary aggregates. Due
to the reduced noise emission of the electric drivetrain however,
new requirements are now imposed on the construction of the au-
xiliary aggregates. AIR CONDITIONING
Vehicles with a significant electric propulsion component cons-
titute a major thermal management challenge from two perspec-
tives: First, by omitting or minimizing the combustion engine a
„no-cost“ heat source and a drive unit for the air conditioner have
been dispensed with. Second, for the battery electric vehicle in
particular, the energy that must be used for air conditioning for
the driver has a tangible impact on the range of the vehicle. Given
the prerequisite of a certain battery size, if the air conditioning
system of a battery electric vehicle is operated in accordance with
today’s procedures, the range that can be achieved with the ve-
hicle is reduced. As illustrated in Fig. 6, this effect becomes more
pronounced the higher the power consumption of the heating or
cooling components is.