General Motors took the wraps off its second-generation Voltec electric-drive system this morning that will power its 2016 Chevrolet Volt range-extended electric car.
Company executives declined to give specifications for power of the two electric motors, the range-extending engine, or range of the final vehicle.
But they did give some percentage improvements and weight reductions for the new powertrain over that used in the current first-generation Volt.
[EDITOR'S NOTE: This article has been expanded from the version first published, with further detail, more images, and the addition of a schematic video showing the operation of the Voltec powertrain.]
Details on the 2016 Volt itself will be released in January at the 2015 Detroit Auto Show.
While the vehicle's lead engineer, Andrew Farah, attended the powertrain event today in Warren, Michigan, he declined to discuss any specifics about the car.
The primary goals for the new powertrain were to improve performance, raise overall efficiency in both electric and range-extended operation, and cut engine noise significantly.
2016 Chevrolet Volt powertrain - electric motors detail advance briefing, Oct 2014
The major technical difference in the 2016 Volt will be that both motors can both power the car and act as generators, whereas in the previous generation, the car was powered by a 111-kW traction motor and the range-extending engine drove a 55-kW generator.
The new system allows the Voltec system to power the vehicle with one or both motors, depending on power demand and overall efficiency.
GM declined to elaborate on the modes in which the car can operate, but acknowledged that the 2016 Volt has five separate modes of operation--against four for the current car.
MORE: 2016 Chevrolet Volt To Launch Next Year: What We Know So Far (to be updated soon)
Those include an all-electric mode and four different combinations of engine and electric motors/generators, but Chevy executives deferred questions about the specifics to a later date.
They also declined to provide the power output for either motor, though they said that the output ratios of the two were roughly proportional to those in the first Volt.
The two motors use the same stator, but use different rotors. The smaller-output, or "A" motor, uses ferrite rather than rare earth metals, cutting overall rare-earth metal use from 3.2 kg to 1.2 kg, and the use of heavy rare earths (primarily dysprosium) from 282 grams to just 40 grams.
The two-motor drive unit is more efficient than its predecessor, operating at 5 to 12 percent more efficiently. GM declined to specify what metrics that referred to.
It's also 100 pounds (45 kg) lighter than the existing system.
Overall, low-speed acceleration is improved by 20 percent, according to the Volt technology team.
2016 Chevrolet Volt powertrain detail - motor and power electronics unit advance briefing, Oct 2014
The range-extending engine is a 1.5-liter four-cylinder version of GM's new Ecotec series of three- and four-cylinder engines.
Importantly to Volt buyers, the new engine is designed to run on regular fuel.
GM chose the larger engine, rather than a turbocharged 1.0-liter, to ensure it continued to provide enough output under extreme circumstances to propel the car with the same performance as in battery mode--unlike the range-extended BMW i3 REx (although GM officials did not say that specifically).
The 2016 Volt will use a version that is uniquely designed for that car. While it shares a fuel system and direct injection with other versions, it includes three unique aspects that will be found only on the Volt.
First is a 12.5-to-1 compression ratio, higher than the standard version's 10.5-to-1, for more efficient combustion.
Second is cooled exhaust-gas recirculation, required to allow the use of regular-grade gasoline while keeping emissions of nitrous oxides within acceptable limits.
Finally, GM fits what it calls wide-authority cam phasers, which allow a broader spread of valve timing to allow the engine to operate in a mode close to the Atkinson Cycle, which reduces back pressure by keeping the inlet valves open longer.
2016 Chevrolet Volt - first teaser image, Aug 2014
That ability boosts efficiency significantly, said Larry Nitz, executive director of transmission and electrification, while cutting only slightly into peak power output under wide-open throttle.
Reducing the noise, vibration, and harshness of the new engine was one primary goal, and GM workers who had ridden in test-mule Volts with the new powertrain said it was almost impossible to tell when the engine switched on.
The new engine has an aluminum block, compared to the cast-iron block of the current range extender, so overall weight of the new engine is no higher than that of the old one.
The new powertrain also has its power electronics, most significantly the inverter, built directly into the transmission rather than mounted separately on the car's body and connected by large orange high-voltage cables.
The inverter is smaller, lighter, and more efficient, and the integrated location contributes to a total weight reduction for the new powertrain of 130 pounds compared to the current generation.
2016 Chevrolet Volt powertrain detail - lithium-ion battery pack - advance briefing, Oct 2014
LG Chem continues as the supplier of lithium-ion cells for the next Volt, but the latest generation of cells have 20-percent increase in volumetric energy density over the cells used in the 2015 Volt, which themselves were new this year.
The number of cells in the battery pack is cut from 288 to 192, still arranged in 96 modules and producing roughly the same total voltage.
The pack is slightly smaller in dimension, but its center of gravity is 10 mm lower and its weight is 30 pounds (13 kg) lower overall.
GM declined to specify the pack's total energy capacity (17,1 kilowatt-hours in the 2015 Volt) or the percentage of the pack that it uses (presently about 65 percent).
Nitz said, however, that the new pack had higher energy capacity and used more of it, presumably indicating an increase in the car's rated electric range above its current 38 miles.
The onboard charger on the 2016 Volt will be "a little" faster than the current 3.3-kW one, but not much. GM said specifically that (DC) fast charging wasn't needed, and that the current charger was satisfactory to its owners.
Company executives said that point is proven by the stats on 120-Volt vs 240-Volt charging.
Nitz noted that GM expected that up to 80 percent of Volt owners would install 240-Volt Level 2 charging stations. In fact, a majority of Volt charging--55 percent--is done using 120-Volt service instead.
That told the team that faster charging just wasn't a high priority for most Volt drivers.
Overall, the Volt team said that feedback from owners of the first-generation Volt guided the refinements made to the next-generation powertrain.
Two factors surprised the team as real-world data began to filter in from 2011 through 2013, according to Farah and Nitz.
First, the owners "craved" miles driven on electricity--and plugged in much more than the daily overnight recharge that the team had expected.
The average Volt, in fact, is recharged 1.4 times every day, with Volt owners taking advantage of both "opportunistic charging" wherever they find it and charging at workplaces.
Second, the "fluid" and instantaneous experience of electric drive was one of the things the owners prized most--against plug-in hybrids that switched on their engines under maximum power demand.
2016 Chevrolet Volt powertrain
The "big battery pack" that permitted electric drive for its entire range, without help from the engine, turned out to be a huge selling point.
The team, they said, asked themselves what they could do to increase the electric miles that Volts logged.
Those figures are now roughly two-thirds of overall miles, and about 80 percent of commute miles. What would it take, they asked, to boost commute miles driven on electricity from 80 to 90 percent?
In the end, GM released a lot of technical details without answering the questions that Volt owners most wanted to know: What's the electric range, and what's the fuel efficiency in range-extending mode?
Those numbers will come in about 10 weeks--but not yet.
The new 2016 Chevrolet Volt will go on sale during the second half of 2015.
General Motors provided airfare, lodging, and meals to enable High Gear Media to bring you this first-person report.