IEEE Electrification Magazine - June 2014 - 19

Normalized Phase Resistance (p.u.)

option two, shown in diamonds, uses a Chevy volt type
TABLe 1. The Du Key Parameters.
motor B traction em, which is a larger diameter shorter
length design with high-energy Pms. additionally, option
Peak axle torque
1,711 Nm
two used a single off-set gearing arrangement (two
Mass (dry/wet)
65/68.5 kg
mechanical axes) to obtain a 6:1 ratio. option three, the
Oil
type
DEXRON HP
selected Chevrolet spark Bev du, shown in squares, is a
coaxial low numerical gear ratio (e.g., 3.17:1) single planetary gearing paired (single mechanical axis) with a smaller
diameter longer length em with a high peak torque and
high-energy Pms.
the ev1 du with a low peak torque, high-speed electric machine yields the best zero to 60 mi/h acceleration
and range at a 10:1. the volt motor B results indicate that
both range and performance are maximized by lowering
the numerical ratio from 9:1 to 6:1. the spark ev em with
its low-speed high-torque density design performs the
best in range and performance at the 3.17:1 ratio and
approaches but does not match the volt motor B design in
performance. it should be noted that the 3.17:1 ratio was
selected over the 3.87:1 ratio in the du because the lower
ratio provided a higher drive cycle range on the ePa
highway and la92 drive cycles. vehicle range was the
Figure 8. The bar-wound stator end turns of the Spark EV motor.
(Photo courtesy of GM.)
key driver as the low drive ratio was picked for the
design of the Chevrolet spark du.
in addition to gear reduction, the spark ev du provides
TABLe 2. The eM Key Parameters.
several other functions including em support structure,
motor cooling, differential split to outputs, park system,
Motor peak torque
540 Nm
range mode switch (Prndl), and accessory support in a
Motor peak power
105 kW
maintenance-free design. Figure 6 shows a cross-sectional
sketch of most of the du components, and Figure 7 outlines
Peak motor speed
4,500 r/min
how all the internal components are integrated into one du.
Nominal dc bus voltage
350 V
For the single planetary gear-set power flow architecture, it
Rated motor current
450 Arms
provides advantages in the park system loading. the central
Motor outer diameter
213 mm
split line location provides a high structural stiffness and
enables the motor assembly to be manufactured as a sepaMotor stack length
125 mm
rate standalone unit. the variable-speed oil pump allows
optimization to the duty cycle and
operation under difficult duty cycles
2
such as steep-grade motor cooling
6,000 r/min
conditions where splash lube designs
1.9
would be challenged.
1.8
Increasing Speed
5,400 r/min
the du was designed to optimize
1.7
the package space, noise, mass, manu4,800 r/min
facturability, application flexibility, and
1.6
Stranded Wounded Resistance
efficiency. it is packaged around the
1.5 4,200
r/min
axle to minimize front vehicle com1.4
partment under hood volume. the du
3,600 r/min
1.3
ships fully sealed for easier vehicle
3,000 r/min
handling and improved reliability. the
1.2 2,400 r/min
side air conditioning mounts and
1.1 1,800 r/min
0 r/min
1,200 r/min
compatibility with standard Prndl
600 r/min
1
linkage also improve the application
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
flexibility. the total du height was
Normalized Phase Current (p.u.)
minimized by reducing the motor
diameter to maintain necessary Figure 9. The ac resistance as a function of the normalized phase current at various EM
ground clearance, and the du axial mechanical speeds.

IEEE Electrific ation Magazine / j une 2 0 1 4

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2014