Back in 2006, when the Chevrolet Volt was first conceived, its extended-range electric (ER-EV) powertrain was originally dubbed E-Flex as its configuration was designed to be flexible. The only part of the system that was constant was the electric drive and the presence of a battery. The architecture was designed so any type of powerplant could be used as a range extender, and over the last three years concepts have been shown with flex-fuel three-cylinder turbos, inline-four diesels and hydrogen fuel cells.
Ultimately, powertrain chief engineer Larry Nitz and his team opted for a normally aspirated 1.4-liter inline-four for the first generation Volt because it offered the best combination of cost and efficiency. However, while working on the first-generation Volt, work on the second-gen model has been happening in parallel. Way back in May 2007 we talked to then-VP for R&D Larry Burns about using an HCCI engine for the Volt since it could be optimized to operate at steady state speeds. He agreed that was certainly one possible direction.
Right now, the top priority for the second-generation Volt is driving down the cost of the powertrain, including the battery. Although automakers are always reluctant to talk about parts pricing, GM's project management VP, Jon Laukner, has hinted on more than one occasion that the Volt pack costs somewhere in the $600 per kilowatt-hour range or under $10,000 for the 16 kWh unit. The goal is to get that cost down below $400 per kWh in the next few years and a combination of increased volumes and LG Chem launching cell production in western Michigan will certainly help to achieve that.
Reducing the cost of the range extender will also play a part. GM's VP of global vehicle engineering, Karl Stracke told Inside Line that smaller range extenders in the 15-18 kilowatt range are part of the strategy and either a two-cylinder piston engine or a single rotor Wankel are possibilities to replace the current inline-four. Volt communications manager Rob Peterson confirmed to Autoblog that a number of different variants are being evaluated, but he wouldn't say if any particular direction has been selected yet.
Powertrain engineering consultant FEV has recently been showing off an ER-EV Fiat 500 with a Wankel range extender. While Wankels are not known for fuel efficiency (quite the opposite, actually), a modern direct injected unit for this type of application could be highly optimized to provide acceptable performance and consumption. A Wankel also has the advantage of being both very compact for its output and vibration-free, making it well suited for this type of application. With the first-generation Volt only expected to have about a three-year life-span, a final decision will likely be made very soon.