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 2014Enlarge Photo
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 2014Enlarge Photo
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.