Volt: The Next Generation

Larry Nitz, executive director of GM Global Transmissions and Electrification, says that owners of the first-generation Chevrolet Volt are “probably one of the most studied groups of vehicle owners” ever. Some 60% of Volt owners are anonymously providing data to GM via OnStar. And thanks to what GM engineers have learned, they are transforming Volt for the next generation.

The top line is this: General Motors has completely transformed the powertrain for the 
Chevrolet Volt, a transformation that is completely unlike what would ordinarily occur for a car that has been in production since just 2010, to say nothing of a car that has a powertrain setup unlike any vehicle that GM had ever built.

The Volt is a plug-in hybrid. It uses electric motors for primary propulsion. The motors are powered by lithium-ion batteries. There is an internal combustion engine. This engine, for the most part, works as a generator to charge the batteries. Its primary purpose, unlike the case with other hybrid systems, is not to drive the wheels. This is why GM refers to the Volt as an “extended range electric vehicle.”

The powertrain in the Volt—the battery, drive unit, engine, and power electronics—is referred to as the “Voltec” system.

And it is this, the Voltec, that has been completely transformed for the forthcoming 2016 Volt.

Transformed as in being from 5 to 12% more efficient and having a two-motor setup that delivers a 20%+ improvement in electric acceleration (there is a two-motor setup in the original Voltec system, but not as efficient).

That, as well as a mass reduction of 100 lb.

(It is also worth noting that in an age when there is considerable concern regarding the use of rare-earth elements for things like EV motors, one of the two motors uses no rare earths—instead it uses a multi-barrier ferrite magnet that, according to Pete Savagian, who heads up GM’s Electric Drive Systems activities, is similar to the magnet used in a starter motor.)

And speaking of more efficient and reduced mass: there is a revised battery cell chemistry (developed with supplier LG Chem [lgchem.com]) that has a decreased number of cells (192 compared with 288 in the original) because they have been able to increase the storage capacity by 20% on a volume basis. The number of seals for the liquid-cooled battery pack has been reduced from 600 to 400. In addition to which, they have reduced the overall mass of the battery pack by 28.6 lb.

According to Bill Wallace, director, Battery Systems, there are nine carryover parts in the battery.

It is also worth noting that Wallace says that his colleagues in the consumer electronics would are jealous at how well LG Chem and GM have been producing the lithium-ion battery cells for the Volt: more than 20 million produced at less than 2 ppm.

They’ve also addressed overall package size of the drive unit, such as integrating the Traction Power Inverter Module—which manages power flow between the battery and the drive motors—into it so that they’ve been able to eliminate the multitude of bright orange cables that used to connect the elements in the system. (This also helps reduce energy loss.) 

According to Savagian, there is a 60% volume reduction in the power electronics and inverter for the next Volt.

Visually, the drive unit appears similar to a front-wheel-drive transmission. And presumably given that, they’re now building the power unit at the GM Warren Transmission Plant, where Hydra-Matic transmissions are produced for a number of GM vehicles, ranging from the Chevrolet Traverse to the Cadillac XTS.

The plant received a $240-million investment for equipment and the refurbishment of 300,000-ft2 of space; 160 jobs were retained for the program. 

The drive unit for the first genera-tion Volt was manufactured in the GM plant in Ramos, Mexico. But now it is in Michigan.

Observes Larry Nitz, GM Global Transmissions and Electrification executive director, who has been working on the Volt program since generation 1, about the location of the transmission plant, “Most of us work down the street at the Tech Center.”

One thing about the second generation Volt powertrain that is bigger is the internal combustion engine that is used as the range extender. They’re using a direct-injected, 1.5-liter four cylinder engine in place of the 1.4-liter that is in the first-generation Volt. Nitz says that the change was made in response to customers wanting an engine that was more powerful and quieter when it turns on.

The 1.5-liter engine is currently being made at a GM plant in Toluca, Mexico, and will be for the first year of vehicle production. Then it will be shifted to the GM Powertrain plant in Flint, Michigan.