IEEE Electrification Magazine - June 2014 - 18
Motor Terminal
Rotor
Park
Stator
Planetary Gearset
Differential
Output Shaft
Figure 6. A diagram of the Chevrolet Spark DU. (Image courtesy of GM.)
x
performance degradation of battery/battery replace-
ment costs
x
low vehicle performance.
Battery energy density improvement, along with the
cost reduction, a wide network of charging stations, and
fast charging, is the key to ev success.
For range extension, an optimized propulsion system
for a Bev must also include an em that is efficient over a
wide range of driving conditions and an efficient mechanical connection from the motor to the wheels. this combination makes the best use of power and energy from the
battery so as to minimize the power and energy requirement on the battery while delivering appealing vehicle
performance and range. at the same time, this combination of em and mechanical connection to the wheels,
known together as the du, must also be lightweight and
Figure 7. The Chevrolet Spark DU. (Image courtesy of GM.)
18
I E E E E l e c t r i f i c ati o n M agaz ine / j un e 2014
compact, in keeping with the need for an efficient vehicle.
the choice of drive ratio is also critical. any choice of drive
ratio makes several system-level tradeoffs and are selected
balancing drive quality, system efficiency, and drive system cost. a description of the Chevrolet spark du that
was designed to achieve some of these requirements
through its efficient designs, is presented next.
Chevrolet Spark Propulsion
System Components
the Chevrolet spark propulsion system comprises
mechanical gearing, a 104-kw high efficiency, high-density
interior Pm motor, power electronics, and a battery pack.
Du Design and Mechanical Gearing
the Chevrolet spark ev's propulsion system is designed to
have competitive range on a wide variety of drive cycles, in
the environmental Protection agency (ePa) urban and
highway as well as us06 and la92 drive cycle. various du
mechanical configurations and electric machine sizes
were studied to select the correct system that met both
range and performance requirements. a sample set of
three du concepts studied in the Chevrolet spark vehicle
are referenced in Figure 5. it is important to note that each
of the three du options shown in Figure 5 were sized to
provide enough peak axle torque for adequate low-speed
vehicle gradeability. also all gear ratio values quoted in
refer to the numerical speed ratio between em and du
axle output speed. option one, shown in triangles, uses the
gm ev1 design, which was a high ratio (e.g., 10:1)
double-offset gearing (three mechanical axes) paired with
a high-speed, low-peak torque induction electric machine.
Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2014
IEEE Electrification Magazine - June 2014 - Cover1
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