[tt] GM Provides Snapshot of State of the Volt; Tracking to Production in Nov 2010

[Brian Atkins]

http://www.greencarcongress.com/2008/04/gm-provides-sna.html

In a day-long briefing at the GM Tech Center in Warren, Michigan, the GM team 
responsible for the Volt provided a snapshot of the current state of development 
of the extended range electric vehicle (earlier post)—which is tracking to 
production in November 2010—to an international group of journalists.

The accelerated development of the Volt is pushing GM to design, to develop and 
to test in parallel the powertrain and the vehicle. Key topics addressed during 
the briefing were the cycle life and calendar life testing of the lithium-ion 
battery pack; the coming integration this month of the first packs into the 
mules; other powertrain and exhaust system issues; aerodynamic modifications to 
support the 40 mile all-electric range; and design issues.

The battery packs and the powertrain. GM has received initial packs from both 
CPI and A123Systems. General parameters of the packs are an energy capacity of 
16 kWh; weight of about 170 kg, length of about 1.8m. The packs, which are based 
on prismatic cells from each company (the prismatic cell is GM’s go-forward 
design choice for energy batteries and perhaps even power batteries, according 
to Denise Gray, Energy Storage Devices and Strategies Director) need to:

     *

       Provide sufficient power to accelerate the vehicle from 0 to 60 in 8.5 
seconds; deliver passing capability; and deliver “predicted driveability”.
     *

       Provide sufficient energy to support a 40-mile all electric range under 
city and highway driving conditions.
     *

       Have a cycle life that supports 150,000 miles under mixed electric 
vehicle (EV) charge depleting and extended range (ER) charge sustaining mods of 
operation.
     *

       Have a calendar life that is more than 10 years under real world conditions.

GM and its suppliers have already undertaken the cell level testing that has 
assessed the capability of each type of cell (CPI uses a manganese spinel 
chemistry, A123Systems a nano-phosphate chemistry) to achieve the required 
vehicle performance along with accelerated life testing and abuse behavior.

GM is currently engaged in pack level testing (cycle life, calendar life, 
temperature and vibration). The third major test set will be the dynamic testing 
of the packs in the mules and then in the production version of the Volt under 
road conditions.

GM also plans to test charge integration under a variety of simulated conditions 
(110V, 220V, presence of appliances such as washer/dryer or freezer in the 
garage, etc.), brownouts, blackouts, and so on.

The dynamic testing will begin following the integration of the first packs into 
E-flex mules (based on the Malibu) later this month. That will proceed in 
parallel with the pack-level tests in the battery lab that will continue for 
almost two more years—the shortest amount of time into which GM could compress 
testing to validate the required 10-year, 150,000-mile lifespan of the packs.

For the cycle testing, GM is using a two-hour combination of the US urban, 
highway and the more demanding US06 cycles for the discharge; re-charging for 
three-hours; and simulating parking for 3 hours. This pattern will run 24x7 for 
two years on each of the packs. Although the packs are designed to be liquid 
cooled, the testing on the packs is being done without the cooling. The battery 
cycling testing is being done at the GM test facilities in Warren and in 
Mainz-Kastel, Germany.

Although the pack is sized overall at 16 kWh, GM plans to only use 8kWh in 
operations—i.e., a state of charge depletion window of around 50% (the pack 
won’t be charged fully to 16 kWh, because with a full pack, the first regen 
event would begin overcharging the battery). That 8 kWh needs to be deliverable 
at the end of the battery’s 10-year life, so GM is providing itself with a 
buffer with the 16 kWh pack.

With future iterations of the powertrain, GM might begin expanding the SOC 
window, or also begin implementing minor changes in the batteries.

Although the sizing of the pack is conservative, GM’s projected consumption of 
200 Wh per mile (8 kWh over 40 miles) is somewhat aggressive. The team is 
confident in that figure, according to Frank Weber, Global Vehicle Chief 
Engineer, Chevrolet Volt and E-Flex Systems, because of the testing, modeling 
and simulation work they’ve already done. Nonetheless, the sizing of the pack 
provides a buffer.

The E-Flex mules that will receive the Li-packs for battery testing have already 
been in operation out at the Proving Grounds for 6 months, according to GM, with 
NiMH packs as the energy storage system. The focus to date with the mules—which 
implement full E-Flex systems—has been bringing them up to the state of 
readiness to accept the Li-ion packs and begin dynamic testing. Work on the 
mules has included:

     *

       Software function and integration testing;
     *

       Preliminary proof of concept; and
     *

       Calibration of the regenerative braking system.

The mules (one of which was on a lift with the Li-ion pack stationed beneath it) 
have been in operation 6 days a week for two shifts a day. GM expects to have a 
fleet of Li-ion equipped mules in operation by the summertime.

Over the next six months, GM will be focused on three primary areas with the 
powertrain: battery state estimation; thermal development; and propulsion 
development. The latter area includes refinement of the all-electric drive mode, 
hardware testing in EV mode, and further development of the power electronics.

GM has yet to finalize its selection of the combustion engine component of the 
power train, although the engine will be from its Family 0 of European 
small-displacement engines (1.0-, 1.2- and 1.4-liter).

GM is opting for a smaller fuel tank than originally conceived to reduce vehicle 
mass. The tank under consideration will still provide a 400-mile combined range, 
and GM decided to do as much as possible to ensure its 40-mile all electric 
range rather than go overboard in other areas, such as extended vehicle range. 
In recognition that the Volt (ideally) will go long periods of time without 
using the engine, GM has modified the fueling system to be able to eliminate 
evaporative emissions.

Aerodynamics. The inflexible design point of delivering 40 miles all-electric 
range under a variety of conditions with sprightly performance have forced GM to 
put a great deal of effort into the refinement of the exterior shape of the 
Volt. The impact of incremental improvements to the coefficient of drag makes a 
significant difference at highway speed—much more so than the weight of the vehicle.

     The electric range of the Chevrolet Volt is most sensitive to improvements 
in aero, which is in contrast to a traditional vehicle program in which mass 
typically plays a larger role.
     —Frank Weber

Changes to the shape of the production Volt compared to the show car that GM was 
prepared to discuss at the briefing included a longer front overhang; more 
rounded front corners, rather than the sharp corners of the show car; a slightly 
higher roof; and some modifications to the rear.

GM showed a 1/3 model of the production design of the Volt in the wind tunnel at 
the company’s aerodynamics lab in Warren, and uncovered small sections (front 
corner, rear corner) of full-size clay models of the production Volt in the 
design studio.

The interior. The shape and placement of the battery has pushed the occupants 
outboard, or to the sides of the vehicle, so the design team worked with the 
sections of the roof structure and doors to enable aerodynamics and provide 
adequate head room. The interior will accommodate a 6-foot 2-inch (99th 
percentile) male comfortably in the front and rear seats.

GM says it is putting a great deal of effort into the development of the 
human-machine interface for the Volt, although no examples of that were shown 
during the briefing.

     We are looking for an i-Phone like experience.
     —Frank Weber

-- 
Brian Atkins
Singularity Institute for Artificial Intelligence
http://www.singinst.org/