|Although the first E-Flex concept—the Volt—is using a combustion engine genset, GM is also at work on a fuel-cell variant that will use the upcoming 5th generation stack. Click to enlarge.|
While it was the introduction of the Chevrolet Volt—a plug-in series hybrid electric drive vehicle (earlier post)—that generated the most excitement at the North American International Auto Show, it is the accompanying announcement of the E-Flex system that is the key, according to Nick Zielinski, chief engineer for the Volt.
The Volt represents the first application of the E-Flex System, a developing vehicle architecture that will encompass a range of compact to intermediate vehicles with all-electric drive systems (the “E”) powered by electricity from a variety of sources (the “Flex”).
Broadly defined, the E-Flex architecture consists of an electric drive motor, on-board storage for electricity (battery or fuel cell), on-board mechanisms for producing electricity, grid charging (plug-in) capability, and the associated power electronics and control systems.
E-Flex vehicles can include the genset-powered plug-in series hybrid (such as the announced Volt), a fuel-cell hybrid, or a pure battery electric vehicle. GM envisions a range of genset options for the E-Flex vehicles, including engines optimized to run on E85 or E100 and biodiesel.
There is much overlap between E-Flex needs and work being done in other parts of GM—specifically fuel cell vehicle development and the mechanical hybrid systems. (In its evolving taxonomy of offerings, GM refers to its existing portfolio of hybrids as “mechanical hybrids”—i.e., the engine provides mechanical drive power in addition to the electric drive power.)
The drive motor in the Volt, for example, is the same system being used in the Equinox Fuel Cell Vehicle. The upcoming 5th generation fuel cell stack that will be applied in a GM fuel cell vehicle will also find its way onto an E-Flex platform.
And although it is not yet determined, it is possible that the battery pack work being done for the development of the Saturn VUE Green Line plug-in two-mode hybrid (earlier post) will also apply to E-Flex vehicles.
Of all the elements, the electric drive—the motor and the controller system—is the farthest along. The technology in the motor is already on the road in the Equinox fuel cell program. We’ve been working the details of those systems—the controls, the inverter—for the last three or four years. We’ve made major advances in motor efficiency, and also in the size of the controls and the inverter, which are substantially smaller than a few years ago. And we have plans in place [in the fuel cell program] for much more compact inverter packages.
The generator itself is technology very similar to the [drive] motor. We feel we can share a lot of the technology between the two—the electronics controls are very similar.
Least mature is the large energy store battery. The new work is more in the battery pack. The challenge is the systems integration of all those cells. One of the key elements of integrating the batter pack system is cooling, and understanding temperature deltas across the pack as your charge it.—Nick Zielinski
In working through battery pack management and control, GM combines simulation-based analysis, hardware cycling tests and then into vehicles for road testing.
We depend very heavily on the computer simulation work, and also depend heavily on component-level testing.—Nick Zielinski
Presumably, the work being done on integration and control—and the development of optimal operating strategies—for the battery packs in the VUE plug-in hybrid will support the more rapid deployment of E-Flex vehicles (and vice versa).
There are organizational intersections where work is done, that can merge together where it makes sense on the E-Flex. We need to come up with the most efficient and highest level of component sharing with E-Flex—and we are setting up the organization to make that happen.—Nick Zielinski