Automotive Engineering - June 2016 - 14

TECHNOLOGY REPORT

All-new Kia Niro hybrid uses its 48V lithium-ion battery pack
for hotel loads, eliminating 12V battery.
draw during each engine shutdown
event has a direct and strong effect on
battery longevity because of the depth
of discharge. If the battery is returned to
a full charge between engine starts, the
effect on battery life is negligible or
nonexistent.
Conversely, the ANL research
showed that battery failure will occur
more quickly if a full charge is never
reached regardless of the number of
engine start cycles. Also, idling was determined to not be an effective method
of recharging the battery because of
low alternator power output; driving is
best. (See http://www.anl.gov/energysystems/publication/stop-and-restarteffects-modern-vehicle-starting-system-components.)
Simply providing the power to regularly restart engines is just one challenge for electrical system designers.
Keeping radios and interior lights at
constant levels-a "buffering" role
played by the 12V battery-is a critical
factor for consumer acceptance of
stop-start vehicles.
"During an auto start, there is a voltage dip in the vehicle's electrical system," Walker said. "In order to maintain
functionality of cabin systems such as
interior lights, there are technologies
that can be added to a vehicle to protect the components against a voltage
dip and maintain customer satisfaction
during an auto start. These technologies include dual batteries, DC/DC converters and ultracapacitors."
14 June 2016

A handful of vehicles already use dual
battery systems to support large numbers of power-hungry features and
functions. It may become more common as more safety critical technologies are combined on vehicles that use
complex fuel-saving techniques.
The 2016 Chevrolet Malibu 2.5-L's
stop-start system, for example, uses two
batteries: a 12V battery under the hood
and a second one mounted in the rear.
The system (equipped with a tandemsolenoid starter for faster starts) is calibrated so that when the ICE shuts off,
the second battery is signaled to handle
the car's hotel loads-i.e., power the
lights, climate control, audio, windows
and door locks. Also, with the engine off
the car's climate control remains on,
albeit operating on reduced power.
"Dual battery systems will become
more common as they provide value in
several ways," Rigby said. "Having two
batteries provides better voltage stability during start-stop events as well as
redundancy to support the high degree
of reliability necessary with advanced
safety systems. In addition, a dual battery, dual-chemistry system allows the
optimization of performance and cost
to deliver the best value for automakers
and consumers."
Often, the second battery is part of a
48V system. Engineering higher-voltage
systems can make it simpler to power
functions such as parking cameras and
integrated sensors. Though going to
48V is beneficial, experts said the

industry trend has been to retain the
12V systems. But at the 2016 Chicago
auto show, Kia unveiled its 2017 Niro
hybrid CUV, which uses its lithium battery pack to power the headlights,
windshield wipers, and other traditional
tasks of the 12V lead-acid battery, which
has been eliminated (see http://articles.
sae.org/14614/).
"Higher voltages help keeping the
peak amperage down," explained
Stefano Zanella, Business Development
Manager at Texas Instruments.
"Batteries are sensitive to the ratio of
their capacity expressed in amp hours
and the load current, increasing their
lifetime and reducing cable size, making
them cheaper and lighter."
A 48V rail will require a DC/DC converter or a second 12V battery, he explained, because there are just too
many 12V components in a car that are
very cheap and cannot be effectively
replaced by 48V components.
Some developers are turning to ultracapacitors to provide quick boosts for
stop-start systems. They can provide
power to turn the engine over without
straining the battery.
"Since ultracapacitors do not rely on
a chemical reaction to supply their energy, ultracapacitors can discharge their
stored energy very quickly," GM's
Walker said. "The 2016 Cadillac ATS and
CTS take advantage of ultracapacitors
to provide a quick energy boost during
the auto start. This burst of energy allows the engine to start faster and helps
in providing a more seamless restart for
the driver."
This design technique can extend the
lifetimes of lead acid batteries. The
Cadillac system, co-developed with
Continental, uses Maxwell Technologies
ultracaps to augment battery power. It
is not available on the ATS-V and CTS-V
performance versions.
"Adding an ultracapacitor lets the
battery deliver significantly lower starting currents, which leads to less degradation of the battery chemistry," said
Jens Keiser, Maxwell's senior product
marketing manager. "Also, the battery
sees fewer high-current peak demands."
Terry Costlow

AUTOMOTIVE ENGINEERING

http://articles.sae.org/14614/ http://articles.sae.org/14614/ http://www.anl.gov/energy-systems/publication/topo-and-restart-effects-modern-vehicle-starting-system-components http://www.anl.gov/energy-systems/publication/topo-and-restart-effects-modern-vehicle-starting-system-components http://www.anl.gov/energy-systems/publication/topo-and-restart-effects-modern-vehicle-starting-system-components

Automotive Engineering - June 2016

Table of Contents for the Digital Edition of Automotive Engineering - June 2016