IEEE Electrification Magazine - June 2014 - 21

a reduced winding temperature compared with a stranded design. this
Y
reduction in end turn temperature
results in a slightly lower winding
resistance and a significantly
increased insulation life.
a wave winding layout is used for
the Chevrolet spark bar-winding stator. this is in contrast with a stranded
design where lap winding is typically
used. during construction the wave
winding pattern is laid out by insertY
ing axially, either by hand or by fully
X
Time = 1
automated robotic process, "hair-pin"
0
20
40 (mm)
segments into the stator slots. a
twisting operation in the forward
(clockwise) and reverse (counterclock- Figure 12. The double barrier rotor geometry of the Spark EV motor.
wise) direction forms a frog-leg-type
shape. these are illustrated in Figure 10(a) and (b), respectivein significant protection against turn-to-turn or turn-toly. the ends are then welded to form the wave winding patground faults that might otherwise occur because of voltage
tern. the manufacturing process can be fully automated,
spikes and/or thermal cycling. the bar-wound construction
resulting in a robust manufacturing process.
reduces effective winding electrical resistance and enables
the Chevrolet spark stator has four conductors (bars) in
the surface of every conductor direct contact to coolant,
each slot as shown in Figure 11(a). a
thereby improving the overall em therB-shaped slot liner [Figure 11(b) and (c)]
mal performance. life testing of the baris used to insulate the conductors from
wound stators at gm shows that such
the steel lamination. this is an
construction outperforms any other
improvement from the earlier design,
types of stator construction.
gm rear-wheel drive two-mode hybrid,
the Chevrolet spark Bev rotor is
where an s-shaped slot liner is used
an iPm type, with magnets arranged
[Figure 11(a)]. the B-shaped slot liner
in a double-barrier v pattern to develeliminates the gaps (to the steel lamiop a combination of magnet torque
nation) that an s-shaped slot liner has
and reluctance torque. a sectional
in the one corner of the conductors,
view of the rotor geometry is shown
thus providing better insulation. as a
in Figure 12. the shape and the placeresult, the spark ev motor exhibits excellent voltage isolament of the barrier are optimized for torque ripple, which
tion, a vital element of motor durability. to further make the
is a major driver for noise and vibration. additional air
bar-wound construction robust to manufacturing variation,
slots also have been added to the rotor, as shown in
the unique wire forms were coated with an insulating epoxy.
Figure 12, to lower torque ripple.
as stated earlier, the combination of end-turn construction
all of these resulted in a low-noise and highly effiand slot liners ensures that no conductor, either in the endcient drive system to meet the requirements set forth for
turn area or in the slot, touches another conductor, resulting
this program.

The battery electric
vehicle is widely
accepted to be
the automobile
of the future.

(a)

(b)

(c)

Figure 13. The Chevrolet Spark power electronics modules: (a) the inverter module, (b) the accessory power supply module, and (c) the battery
charger module. (Photos courtesy of GM.)

IEEE Electrific ation Magazine / j une 2 0 1 4

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