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2.2.2.2 ELECTRICAL MACHINE
The electrical machine can extend and improve the combustion
engine as a propulsion source (improvement of the efficiency of
combustion engine machines in partial load range for hybrids), or
can also completely replace the combustion engine (for example,
in the REEV, BEV, and FCEV concepts). Use of the term „electrical
machine“ is appropriate, as most of the electric propulsion systems
can drive the engine, as well as the generator for energy recovery.
CHARACTERISTICS
Due to its torque characteristics the electric motor is outstandin-
gly suited for use as the propulsion engine in vehicles: Maximum
torque is available from 0 rpm, it remains constant up to a specific
rpm and only drops thereafter (field weakening range). Conse-
quently, a clutch can be dispensed with and only a transmission
gearing unit is required. Additional advantages are high efficiency
(as much as 95 percent), problem-free partial load range, torque
from standstill, recuperation possibility, robustness, long service
life, low maintenance costs, good scalability and a relatively low
noise level. Moreover, the motor can also be operated for a speci-
fic period of time above the actual nominal power (overload range)
without damage.
THREE-PHASE MOTORS
Three-phase machines are AC machines with 3-phase alternating
current. The rotating-field windings are in the stator (also stati-
onary armature) of the motor. The three alternating voltages are
each offset by 120 degrees and feed the windings with the resul-
tant currents. In the vehicle, to achieve this, the direct current from
the battery must be converted into a 3-phase alternating current
and then the electric motor can be activated appropriately for the
situation. So-called inverters are required for this. This generates a
rotary magnetic field inside the motor, which is followed by the rotor.
Fig. 9: The wellness temperature of battery cells
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10 see Tübke (2008a)
11 Author’s own illustration
Fig. 10: Torque and power curves compared
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