Chevrolet Volt chief engineer Andrew Farah
is among those making the round trip from the Milford Proving Ground
through Ohio, Pennsylvania, Maryland, West Virginia, before returning
home. The drive will take a few days and will require
approximately 4 tanks of gas.
The drive is dubbed the
"65-Percent Drive" according to Autoblog, which in
GM-speak means the test drive made when 65 percent of the vehicle's
hardware and software is done. Reportedly, GM is actually about
90 percent done, but is just sticking to its traditional naming.
GM will complete 70, 80, 90 and 100 percent drives in coming
One thing GM is still tweaking is how much power from
the gas-engine generator to put directly to the electric drive motor,
versus using the generator power to charge the batteries. GM is
finding that frequently putting the power directly to the motor
improves performance. However, the generator will still charge
the batteries in some cases, as well.
The engine will be run
between 1,200 and 4,000 rpm, using factors like speed and power load
requirements to decide on the necessary speed. GM wants to keep
the engine between 30 to 100 percent load, as higher loads reduce
pumping losses. GM was tight lipped about fuel economy under
the old method (sustained charge) or the new method (variable speed,
some power going directly to the electric motor).
company did say that the prototypes are getting good
mileage -- over 300 miles on a tank of gas -- when operating in
generator mode. This is in addition to the vehicle's 40 mile
all-electric range. Another interesting test will be when GM
runs the car's gas engine on E85 ethanol fuel. The vehicles are
FlexFuel designs, so they can enjoy both gas and ethanol.
to the battery mode, the
batteries are performing well and aren't getting too cold or too
hot, both conditions which can degrade performance. The cars
aren't yet reaching the 40 mile target on a charge, but GM expects to
pass that milestone on the next test, with tweaking. On the
trip, GM is testing vehicles both running on a depleted battery
charge, and a full charge.
GM is also looking to fine tune and
minimize noise, vibration, and harshness (NVH). Currently, the
gas engine typically won't turn on until the car is moving, at which
point the noise will be drowned out by the wind and road noises.
GM, nonetheless, is pleased with the performance, and plans to
further reduce NVH by tweaking vehicle parameters that effect the
road and wind noise.
Other GM engineers were off testing Volts
at Pikes Peak in Colorado. One key concern is whether the Volt
will reach a "tipping point", where the gas engine can't
sustain battery charging, and the battery becomes depleted below the
typical minimum of 30 percent charge. Even a strenuous 14-mile
trip to the 14,000-foot summit was unable to overwhelm the 100 hp
generator, though, so it appears that the "tipping point"
will never be reached in real world situations -- if GM's
claims hold true.
A critical test to come will be how the
vehicle performs in cold weather. In cold weather, the Volt
starts with the generator running, to help heat up vehicle and
jump-start performance. Battery performance typically suffers
incrementally worse degradation, the colder it gets (this is a major
argument for ultracapacitors which perform favorably, but are more
quote: GM wants to keep the engine between 30 to 100 percent load, as higher loads reduce pumping losses
quote: The small gas engine on the Volt does not have a throttle. It is either on and running or off.
quote: This allows it to be tuned to operate at peak efficiency and without the additional complexity typical automobile engine have.